Admittance matrix (Knotenpotentialverfahren)

pom.xml

@@ -35,6 +35,11 @@
       <artifactId>jackson-databind</artifactId>
       <version>2.17.0</version>
     </dependency>
+    <dependency>
+      <groupId>org.apache.commons</groupId>
+      <artifactId>commons-math3</artifactId>
+      <version>3.6.1</version>
+    </dependency>
   </dependencies>
 
 </project>

src/main/java/de/ph87/electro/CONFIG.java

@@ -6,9 +6,7 @@ import static java.lang.Math.round;
 
 public class CONFIG {
 
-  public static final double BULB_VOLTAGE_MIN = 0.5;
+  public static final double VOLTAGE_HIGH_MIN = 0.1;
-
-  public static final double VOLTAGE = 3.0;
 
   public static final int RASTER = 200;
 

src/main/java/de/ph87/electro/circuit/Calculation.java

@@ -0,0 +1,216 @@
+package de.ph87.electro.circuit;
+
+import de.ph87.electro.circuit.part.InnerConnection;
+import de.ph87.electro.circuit.part.Junction;
+import de.ph87.electro.circuit.part.Part;
+import de.ph87.electro.circuit.part.parts.PartBattery;
+import de.ph87.electro.circuit.part.parts.PartLight;
+import lombok.Getter;
+import lombok.NonNull;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.commons.math3.linear.*;
+
+import java.util.Collections;
+import java.util.List;
+
+import static java.lang.Math.max;
+
+@Slf4j
+@Getter
+public class Calculation {
+
+  private static final double NO_RESISTANCE = 1e-12;
+
+  private static final double FULL_ADMITTANCE = 1 / NO_RESISTANCE;
+
+  private final List<Junction> junctions;
+
+  private final RealMatrix matrix;
+
+  private final RealVector currents;
+
+  private RealVector potentials = null;
+
+  public Calculation(final int numNodes) {
+    junctions = Collections.emptyList();
+    matrix = new Array2DRowRealMatrix(numNodes, numNodes);
+    currents = new ArrayRealVector(numNodes);
+  }
+
+  public Calculation(final Circuit circuit) {
+    final PartBattery pivot = circuit.streamParts().flatMap(PartBattery::filterCast).findFirst().orElseThrow(RuntimeException::new);
+    junctions = circuit.streamJunctions().filter(junction -> junction != pivot.getMinus()).toList(); // pivot.minus is GND and cannot be part of the matrix (linear dependency)
+    matrix = new Array2DRowRealMatrix(junctions.size(), junctions.size());
+    currents = new ArrayRealVector(junctions.size());
+    fromSchematic(circuit);
+    solve();
+    toSchematic(circuit);
+  }
+
+  private void fromSchematic(final Circuit circuit) {
+    circuit.streamWires().forEach(
+      wire -> addResistor(wire.getA(), wire.getB(), NO_RESISTANCE)
+    );
+    circuit.streamParts().forEach(part -> {
+      for (final InnerConnection innerConnection : part.getInnerConnections()) {
+        addResistor(innerConnection.a, innerConnection.b, NO_RESISTANCE);
+      }
+      if (part instanceof final PartBattery battery) {
+        addBattery(battery);
+      } else if (part instanceof final PartLight light) {
+        addResistor(light.getA(), light.getB(), light.getResistance());
+      }
+    });
+  }
+
+  private void toSchematic(final Circuit circuit) {
+    circuit.streamJunctions().forEach(junction -> junction.setVoltage(getPotential(junction)));
+    circuit.streamWires().forEach(wire -> wire.setCurrent(getCurrent(wire)));
+    circuit.streamParts().forEach(Part::postCalculate);
+  }
+
+  private double getPotential(final @NonNull Junction junction) {
+    final int index = getJunctionIndex(junction);
+    if (index < 0) {
+      return 0; // per definition
+    }
+    if (potentials == null) {
+      return Double.NaN;
+    }
+    return potentials.getEntry(index);
+  }
+
+  private double getCurrent(final Wire wire) {
+    final int indexA = getJunctionIndex(wire.getA());
+    final int indexB = getJunctionIndex(wire.getB());
+    final double conductance = indexA >= 0 && indexB >= 0 ? matrix.getEntry(indexA, indexB) : FULL_ADMITTANCE;
+    final double potentialDifference = getPotential(wire.getB()) - getPotential(wire.getA());
+    return conductance * potentialDifference;
+  }
+
+  private int getJunctionIndex(@NonNull final Junction junction) {
+    for (int i = 0; i < junctions.size(); i++) {
+      if (junctions.get(i) == junction) {
+        return i;
+      }
+    }
+    return -1;
+  }
+
+  public void addResistor(final Junction a, final Junction b, final double resistance) {
+    final int indexA = getJunctionIndex(a);
+    final int indexB = getJunctionIndex(b);
+    addResistor(indexA, indexB, resistance);
+  }
+
+  public void addResistor(final int index0, final int index1, double resistance) {
+    double conductance = 1.0 / resistance;
+    if (index0 >= 0) {
+      matrix.setEntry(index0, index0, matrix.getEntry(index0, index0) + conductance);
+    }
+    if (index1 >= 0) {
+      matrix.setEntry(index1, index1, matrix.getEntry(index1, index1) + conductance);
+    }
+    if (index0 >= 0 && index1 >= 0) {
+      matrix.setEntry(index0, index1, matrix.getEntry(index0, index1) - conductance);
+      matrix.setEntry(index1, index0, matrix.getEntry(index1, index0) - conductance);
+    }
+    potentials = null;
+  }
+
+  public void addBattery(final PartBattery battery) {
+    final double current = battery.getVoltage() / battery.getResistance();
+    final int indexMinus = getJunctionIndex(battery.getMinus());
+    final int indexPlus = getJunctionIndex(battery.getPlus());
+    addCurrentSource(indexMinus, indexPlus, current, battery.getResistance());
+  }
+
+  public void addCurrentSource(final int index0, final int index1, final double current, final double resistance) {
+    if (index0 >= 0) {
+      currents.setEntry(index0, currents.getEntry(index0) - current);
+    }
+    if (index1 >= 0) {
+      currents.setEntry(index1, currents.getEntry(index1) + current);
+    }
+    addResistor(index0, index1, resistance);
+    potentials = null;
+  }
+
+  public void solve() {
+    final DecompositionSolver solver = new LUDecomposition(matrix).getSolver();
+    try {
+      potentials = solver.solve(currents);
+    } catch (SingularMatrixException e) {
+      potentials = null;
+      log.error("Schaltung fehlerhaft: {}", e.getMessage());
+    }
+  }
+
+  @Override
+  public String toString() {
+    final Format matrixFormat = new Format(matrix);
+    final Format currentsFormat = new Format(currents);
+    final Format potentialsFormat = new Format(potentials);
+
+    final StringBuilder builder = new StringBuilder();
+    for (int row = 0; row < matrix.getRowDimension(); row++) {
+      builder.append("[");
+      String prefix = "";
+      for (int c = 0; c < matrix.getColumnDimension(); c++) {
+        builder.append(prefix);
+        builder.append(matrixFormat.format(matrix.getEntry(row, c)));
+        prefix = ", ";
+      }
+
+      final String potentialString = potentialsFormat.format(potentials.getEntry(row));
+      final String currentString = currentsFormat.format(currents.getEntry(row));
+      builder.append("] x [%s V] = [%s A]\n".formatted(potentialString, currentString));
+    }
+    return builder.toString();
+  }
+
+  @Getter
+  private static final class Format {
+
+    private int integer;
+
+    private int decimal;
+
+    private final String format;
+
+    public Format(final RealMatrix matrix) {
+      for (int r = 0; r < matrix.getRowDimension(); r++) {
+        for (int c = 0; c < matrix.getColumnDimension(); c++) {
+          append(matrix.getEntry(r, c));
+        }
+      }
+      format = calculateFormat();
+    }
+
+    public Format(final RealVector vector) {
+      for (int r = 0; r < vector.getDimension(); r++) {
+        append(vector.getEntry(r));
+      }
+      format = calculateFormat();
+    }
+
+    private void append(final double value) {
+      final String string = "%+f".formatted(value);
+      final String[] parts = string.split("[.,]");
+      integer = max(integer, parts[0].length());
+      if (parts.length > 1) {
+        decimal = max(decimal, parts[1].length());
+      }
+    }
+
+    private String calculateFormat() {
+      return "%%+%d.%df".formatted(integer + decimal + (decimal > 0 ? 1 : 0), decimal);
+    }
+
+    public String format(final double value) {
+      return format.formatted(value);
+    }
+
+  }
+
+}

src/main/java/de/ph87/electro/circuit/Circuit.java

@@ -4,7 +4,6 @@ import de.ph87.electro.circuit.part.Junction;
 import de.ph87.electro.circuit.part.Part;
 import de.ph87.electro.circuit.part.PartDto;
 import de.ph87.electro.circuit.part.Position;
-import de.ph87.electro.circuit.part.parts.PartBattery;
 import lombok.NoArgsConstructor;
 import lombok.NonNull;
 
@@ -18,6 +17,8 @@ public class Circuit {
 
   private final List<Part> parts = new ArrayList<>();
 
+  private final List<Junction> junctions = new ArrayList<>();
+
   private final List<Wire> wires = new ArrayList<>();
 
   public Circuit(final CircuitDto dto) {
@@ -41,25 +42,17 @@ public class Circuit {
   }
 
   public void evaluateAndRender() {
-    parts.forEach(Part::reset);
+    new Calculation(this);
-    streamBatteries().forEach(PartBattery::startPropagation);
     parts.forEach(Part::render);
   }
 
-  private Stream<PartBattery> streamBatteries() {
-    return parts.stream().filter(part -> part instanceof PartBattery).map(part -> (PartBattery) part);
-  }
-
-  public Stream<Wire> streamWires() {
-    return wires.stream();
-  }
-
   public <T extends Part> T addPart(final T part) {
     if (parts.contains(part)) {
       throw new RuntimeException();
     }
     if (isFree(part.getPosition())) {
       parts.add(part);
+      junctions.addAll(part.getJunctions());
       part.render();
     }
     return part;
@@ -82,6 +75,14 @@ public class Circuit {
     return parts.stream();
   }
 
+  public Stream<Junction> streamJunctions() {
+    return junctions.stream();
+  }
+
+  public Stream<Wire> streamWires() {
+    return wires.stream();
+  }
+
   public int getPartCount() {
     return parts.size();
   }

src/main/java/de/ph87/electro/circuit/CircuitPanel.java

@@ -1,6 +1,8 @@
 package de.ph87.electro.circuit;
 
 import de.ph87.electro.circuit.part.Position;
+import de.ph87.electro.circuit.part.parts.PartBattery;
+import de.ph87.electro.circuit.part.parts.PartLight;
 
 import javax.swing.*;
 import java.awt.*;
@@ -15,6 +17,19 @@ public class CircuitPanel extends JPanel {
 
   public CircuitPanel() {
     new CircuitPanelDropTarget(this, circuit);
+    final PartBattery battery = circuit.addPart(new PartBattery(Position.ofRaster(1, 0)));
+
+    final PartLight light0 = circuit.addPart(new PartLight(Position.ofRaster(0, 2)));
+    light0.clockwise();
+
+    final PartLight light1 = circuit.addPart(new PartLight(Position.ofRaster(1, 2)));
+    light1.clockwise();
+    light1.clockwise();
+    light1.clockwise();
+
+    circuit.connect(battery.getMinus(), light0.getA());
+    circuit.connect(light0.getB(), light1.getA());
+    circuit.connect(light1.getB(), battery.getPlus());
   }
 
   @Override
@@ -51,13 +66,7 @@ public class CircuitPanel extends JPanel {
   }
 
   private void drawWires(final Graphics2D g) {
-    circuit.streamWires().forEach(wire -> {
+    circuit.streamWires().forEach(wire -> wire.draw(g));
-      final Position a = wire.getA().getPosition();
-      final Position b = wire.getB().getPosition();
-      g.setColor(wire.getA().getColor());
-      g.setStroke(WIRE_STROKE);
-      g.drawLine(a.absolute.x, a.absolute.y, b.absolute.x, b.absolute.y);
-    });
   }
 
 }

src/main/java/de/ph87/electro/circuit/Wire.java

@@ -2,18 +2,33 @@ package de.ph87.electro.circuit;
 
 import de.ph87.electro.circuit.part.Junction;
 import de.ph87.electro.circuit.part.Position;
-import lombok.Data;
+import lombok.Getter;
 import lombok.NonNull;
+import lombok.Setter;
+import lombok.ToString;
 
-@Data
+import java.awt.*;
+import java.awt.geom.Rectangle2D;
+
+import static de.ph87.electro.CONFIG.LABEL_FONT;
+import static de.ph87.electro.CONFIG.WIRE_STROKE;
+import static java.lang.Math.abs;
+import static java.lang.Math.round;
+
+@ToString
 public class Wire {
 
+  @Getter
   @NonNull
   private final Junction a;
 
+  @Getter
   @NonNull
   private final Junction b;
 
+  @Setter
+  private double current = Double.NaN;
+
   public Wire(@NonNull final Junction a, @NonNull final Junction b) {
     this.a = a;
     this.b = b;
@@ -34,4 +49,34 @@ public class Wire {
     throw new RuntimeException();
   }
 
+  public double getCurrent(final Junction junction) {
+    return junction == a ? current : -current;
+  }
+
+  public void draw(final Graphics2D g) {
+    g.setColor(a.getColor());
+    g.setStroke(WIRE_STROKE);
+    g.drawLine(a.getPosition().absolute.x, a.getPosition().absolute.y, b.getPosition().absolute.x, b.getPosition().absolute.y);
+
+    drawValues(g, "%.2f A".formatted(abs(current)), -0.5);
+    drawValues(g, "%.2f V".formatted(a.getVoltage()), +0.5);
+  }
+
+  private void drawValues(final Graphics2D g, final String string, final double offset) {
+    g.setFont(LABEL_FONT);
+    final Rectangle2D bounds = g.getFontMetrics().getStringBounds(string, g);
+    final int mx = (a.getPosition().absolute.x + b.getPosition().absolute.x) / 2;
+    final int my = (a.getPosition().absolute.y + b.getPosition().absolute.y) / 2;
+
+    final int bx = (int) round((mx - bounds.getWidth() / 2)) - 2;
+    final int by = (int) round((my - bounds.getHeight() / 2) + offset * bounds.getHeight()) - 2;
+    g.setColor(new Color(255, 255, 255, 200));
+    g.fillRect(bx, by, (int) round(bounds.getWidth()) + 4, (int) round(bounds.getHeight()) + 4);
+
+    final int sx = (int) round((mx - bounds.getWidth() / 2));
+    final int sy = (int) round(my + bounds.getHeight() / 3 + offset * bounds.getHeight());
+    g.setColor(a.getColor());
+    g.drawString(string, sx, sy);
+  }
+
 }

src/main/java/de/ph87/electro/circuit/part/InnerConnection.java

@@ -0,0 +1,14 @@
+package de.ph87.electro.circuit.part;
+
+public class InnerConnection {
+
+  public final Junction a;
+
+  public final Junction b;
+
+  public InnerConnection(final Junction a, final Junction b) {
+    this.a = a;
+    this.b = b;
+  }
+
+}

src/main/java/de/ph87/electro/circuit/part/Junction.java

@@ -1,9 +1,7 @@
 package de.ph87.electro.circuit.part;
 
-import de.ph87.electro.circuit.ShortCircuit;
 import de.ph87.electro.circuit.Wire;
 import lombok.Getter;
-import lombok.Setter;
 import lombok.ToString;
 
 import java.awt.*;
@@ -32,7 +30,6 @@ public class Junction {
 
   private final Set<Wire> wires = new HashSet<>();
 
-  @Setter
   @ToString.Include
   private double voltage = Double.NaN;
 
@@ -60,31 +57,9 @@ public class Junction {
     updatePosition();
   }
 
-  public void reset() {
+  public void setVoltage(final double voltage) {
-    voltage = Double.NaN;
+    this.voltage = voltage;
-    color = VOLTAGE_UNKNOWN_COLOR;
+    this.color = Double.isNaN(voltage) ? VOLTAGE_UNKNOWN_COLOR : ((voltage >= VOLTAGE_HIGH_MIN) ? VOLTAGE_HIGH_COLOR : VOLTAGE_LOW_COLOR);
-  }
-
-  public void propagate(final double newVoltage) throws ShortCircuit {
-    if (voltage == newVoltage) {
-      return;
-    }
-    if (Double.isNaN(voltage)) {
-      voltage = newVoltage;
-      if (Double.isNaN(voltage)) {
-        color = Color.GRAY;
-      } else if (voltage > 0) {
-        color = VOLTAGE_HIGH_COLOR;
-      } else {
-        color = VOLTAGE_LOW_COLOR;
-      }
-      owner.propagate(this);
-      for (Wire wire : wires) {
-        wire.getOpposite(this).propagate(newVoltage);
-      }
-      return;
-    }
-    throw new ShortCircuit();
   }
 
   public void render(final Render g) {

src/main/java/de/ph87/electro/circuit/part/Part.java

@@ -1,16 +1,13 @@
 package de.ph87.electro.circuit.part;
 
-import de.ph87.electro.circuit.ShortCircuit;
 import de.ph87.electro.circuit.part.parts.*;
 import lombok.Getter;
 import lombok.Setter;
 import lombok.ToString;
 
 import java.awt.*;
-import java.util.ArrayList;
 import java.util.List;
-import java.util.Optional;
+import java.util.*;
-import java.util.UUID;
 
 import static de.ph87.electro.CONFIG.PART_BACKGROUND;
 import static de.ph87.electro.CONFIG.RASTER;
@@ -29,17 +26,16 @@ public abstract class Part {
 
   private Position position;
 
-  private Orientation orientation;
+  private Orientation orientation = Orientation.R0;
 
   private final List<Junction> junctions = new ArrayList<>();
 
   protected final Render render = new Render();
 
-  protected Part(final String name, final Position position, final Orientation orientation) {
+  protected Part(final String name, final Position position) {
     this.uuid = UUID.randomUUID().toString();
     this.name = name;
     setPosition(position);
-    this.orientation = orientation;
   }
 
   protected Part(final PartDto dto) {
@@ -73,10 +69,6 @@ public abstract class Part {
     render();
   }
 
-  public void reset() {
-    junctions.forEach(Junction::reset);
-  }
-
   public void render() {
     render.rect(ZERO, RASTER, RASTER, null, null, PART_BACKGROUND);
 
@@ -106,7 +98,7 @@ public abstract class Part {
     // may be overwritten
   }
 
-  public void propagate(final Junction source) throws ShortCircuit {
+  public void postCalculate() {
     // may be overwritten
   }
 
@@ -132,4 +124,8 @@ public abstract class Part {
     };
   }
 
+  public List<InnerConnection> getInnerConnections() {
+    return Collections.emptyList();
+  }
+
 }

src/main/java/de/ph87/electro/circuit/part/PartOther.java

@@ -2,8 +2,8 @@ package de.ph87.electro.circuit.part;
 
 public abstract class PartOther extends Part {
 
-  protected PartOther(final String name, final Position position, final Orientation orientation) {
+  protected PartOther(final String name, final Position position) {
-    super(name, position, orientation);
+    super(name, position);
   }
 
   protected PartOther(final PartDto dto) {

src/main/java/de/ph87/electro/circuit/part/Position.java

@@ -28,6 +28,10 @@ public final class Position {
     this.inside = new Point(x % RASTER, y % RASTER);
   }
 
+  public static Position ofRaster(final int x, final int y) {
+    return new Position(x * RASTER, y * RASTER);
+  }
+
   @Override
   public int hashCode() {
     return absolute.hashCode();

src/main/java/de/ph87/electro/circuit/part/Render.java

@@ -61,11 +61,13 @@ public class Render {
     }
   }
 
-  public void textCenter(final Font font, final String string, final int y, final Color color) {
+  public void textCenter(final Font font, final String string, final int innerX, final int innerY, final Color color) {
     g.setFont(font);
     g.setColor(color);
     final Rectangle2D bounds = g.getFontMetrics().getStringBounds(string, g);
-    g.drawString(string, (int) round(RASTER - bounds.getWidth()) / 2, y + g.getFont().getSize());
+    final int x = innerX - (int) round(bounds.getWidth()) / 2;
+    final int y = innerY + (int) round(bounds.getHeight()) / 2;
+    g.drawString(string, x, y);
   }
 
   public void clockwise(final Orientation orientation) {

src/main/java/de/ph87/electro/circuit/part/parts/PartBattery.java

@@ -1,6 +1,5 @@
 package de.ph87.electro.circuit.part.parts;
 
-import de.ph87.electro.circuit.ShortCircuit;
 import de.ph87.electro.circuit.part.Junction;
 import de.ph87.electro.circuit.part.Orientation;
 import de.ph87.electro.circuit.part.Part;
@@ -10,11 +9,12 @@ import lombok.Setter;
 import lombok.ToString;
 
 import java.awt.*;
+import java.util.stream.Stream;
 
 import static de.ph87.electro.CONFIG.*;
 
 @Getter
-@ToString(callSuper = true)
+@ToString(callSuper = true, onlyExplicitlyIncluded = true)
 public class PartBattery extends Part {
 
   private static final double MINUS_W = 0.1 * RASTER;
@@ -32,24 +32,21 @@ public class PartBattery extends Part {
   private final Junction plus;
 
   @Setter
-  private double voltage;
+  @ToString.Include
+  private double voltage = 3;
 
-  private ShortCircuit shortCircuit = null;
+  @Setter
+  @ToString.Include
+  private double resistance = 0.05;
 
   public PartBattery() {
     this(Position.ZERO);
   }
 
   public PartBattery(final Position position) {
-    this("Batterie", position, Orientation.R0, VOLTAGE);
+    super("Batterie", position);
-  }
+    minus = newJunction(this, "PLUS", P10, P50);
-
+    plus = newJunction(this, "MINUS", P90, P50);
-  public PartBattery(final String name, final Position position, final Orientation orientation, final double initialVoltage) {
-    super(name, position, orientation);
-    minus = newJunction(this, "-", P10, P50);
-    plus = newJunction(this, "+", P90, P50);
-    voltage = initialVoltage;
-    startPropagation();
   }
 
   public PartBattery(final PartBatteryDto dto) {
@@ -57,17 +54,6 @@ public class PartBattery extends Part {
     minus = newJunction(this, dto.getMinus(), P10, P50);
     plus = newJunction(this, dto.getPlus(), P90, P50);
     voltage = dto.getVoltage();
-    startPropagation();
-  }
-
-  public void startPropagation() {
-    try {
-      shortCircuit = null;
-      minus.propagate(0);
-      plus.propagate(voltage);
-    } catch (ShortCircuit e) {
-      shortCircuit = e;
-    }
   }
 
   @Override
@@ -81,20 +67,22 @@ public class PartBattery extends Part {
 
   @Override
   protected void _labels() {
+    final int x = RASTER / 2;
     final int y0;
-    final int y1;
     if (getOrientation() == Orientation.R180) {
       y0 = P95 - LABEL_FONT.getSize();
-      y1 = P05;
     } else {
       render.clockwise(getOrientation());
       y0 = P05;
-      y1 = P95 - LABEL_FONT.getSize();
     }
-    render.textCenter(LABEL_FONT, "%.1fV".formatted(voltage), y0, Color.BLACK);
+    render.textCenter(LABEL_FONT, "%.1fV".formatted(voltage), x, y0, Color.BLACK);
-    if (shortCircuit != null) {
+  }
-      render.textCenter(LABEL_FONT, "KURZSCHLUSS", y1, Color.RED);
+
+  public static Stream<PartBattery> filterCast(final Part part) {
+    if (part instanceof final PartBattery battery) {
+      return Stream.of(battery);
     }
+    return Stream.empty();
   }
 
 }

src/main/java/de/ph87/electro/circuit/part/parts/PartJunctionCorner.java

@@ -1,13 +1,13 @@
 package de.ph87.electro.circuit.part.parts;
 
 import de.ph87.electro.circuit.part.Junction;
-import de.ph87.electro.circuit.part.Orientation;
 import de.ph87.electro.circuit.part.PartOther;
 import de.ph87.electro.circuit.part.Position;
 import lombok.Getter;
 import lombok.ToString;
 
-import static de.ph87.electro.CONFIG.*;
+import static de.ph87.electro.CONFIG.P10;
+import static de.ph87.electro.CONFIG.P90;
 
 @Getter
 @ToString(callSuper = true)
@@ -22,13 +22,9 @@ public class PartJunctionCorner extends PartOther {
   }
 
   public PartJunctionCorner(final Position position) {
-    this("", position, Orientation.R0);
+    super("", position);
-  }
+    j0 = newJunction(this, "J0", P10, P10);
-
+    j1 = newJunction(this, "J1", P90, P90);
-  public PartJunctionCorner(final String name, final Position position, final Orientation orientation) {
-    super(name, position, orientation);
-    j0 = newJunction(this, "", P10, P10);
-    j1 = newJunction(this, "", P90, P90);
   }
 
   public PartJunctionCorner(final PartJunctionCornerDto dto) {

src/main/java/de/ph87/electro/circuit/part/parts/PartJunctionEdge.java

@@ -1,14 +1,13 @@
 package de.ph87.electro.circuit.part.parts;
 
 import de.ph87.electro.circuit.part.Junction;
-import de.ph87.electro.circuit.part.Orientation;
 import de.ph87.electro.circuit.part.PartOther;
 import de.ph87.electro.circuit.part.Position;
 import lombok.Getter;
 import lombok.ToString;
 
-import static de.ph87.electro.CONFIG.P50;
 import static de.ph87.electro.CONFIG.P10;
+import static de.ph87.electro.CONFIG.P50;
 
 @Getter
 @ToString(callSuper = true)
@@ -23,13 +22,9 @@ public class PartJunctionEdge extends PartOther {
   }
 
   public PartJunctionEdge(final Position position) {
-    this("", position, Orientation.R0);
+    super("", position);
-  }
+    j0 = newJunction(this, "J0", P10, P50);
-
+    j1 = newJunction(this, "J1", P50, P10);
-  public PartJunctionEdge(final String name, final Position position, final Orientation orientation) {
-    super(name, position, orientation);
-    j0 = newJunction(this, "", P10, P50);
-    j1 = newJunction(this, "", P50, P10);
   }
 
   public PartJunctionEdge(final PartJunctionEdgeDto dto) {

src/main/java/de/ph87/electro/circuit/part/parts/PartJunctionMiddle.java

@@ -1,7 +1,6 @@
 package de.ph87.electro.circuit.part.parts;
 
 import de.ph87.electro.circuit.part.Junction;
-import de.ph87.electro.circuit.part.Orientation;
 import de.ph87.electro.circuit.part.PartOther;
 import de.ph87.electro.circuit.part.Position;
 import lombok.Getter;
@@ -20,12 +19,8 @@ public class PartJunctionMiddle extends PartOther {
   }
 
   public PartJunctionMiddle(final Position position) {
-    this("", position, Orientation.R0);
+    super("", position);
-  }
+    junction = newJunction(this, "J", P50, P50);
-
-  public PartJunctionMiddle(final String name, final Position position, final Orientation orientation) {
-    super(name, position, orientation);
-    junction = newJunction(this, "", P50, P50);
   }
 
   public PartJunctionMiddle(final PartJunctionMiddleDto dto) {

src/main/java/de/ph87/electro/circuit/part/parts/PartLight.java

@@ -33,17 +33,19 @@ public class PartLight extends PartOther {
 
   private static final Color BULB_OFF_COLOR = Color.DARK_GRAY;
 
-  private final Junction pin0;
+  private final Junction a;
 
-  private final Junction pin1;
+  private final Junction b;
 
-  private final double minVoltage;
+  private double resistance = 15;
 
-  private final double maxVoltage;
+  private double minVoltage = 1;
+
+  private double maxVoltage = 3;
 
   private boolean defect = false;
 
-  private double voltage = 0;
+  private double potentialDifference = Double.NaN;
 
   private Color color = BULB_OFF_COLOR;
 
@@ -52,21 +54,16 @@ public class PartLight extends PartOther {
   }
 
   public PartLight(final Position position) {
-    this("Licht", position, Orientation.R0, BULB_VOLTAGE_MIN, VOLTAGE);
+    super("Licht", position);
-  }
+    a = newJunction(this, "A", P10, P50);
-
+    b = newJunction(this, "B", P90, P50);
-  public PartLight(final String name, final Position position, final Orientation orientation, final double minVoltage, final double maxVoltage) {
-    super(name, position, orientation);
-    this.minVoltage = minVoltage;
-    this.maxVoltage = maxVoltage;
-    pin0 = newJunction(this, "", P10, P50);
-    pin1 = newJunction(this, "", P90, P50);
   }
 
   public PartLight(final PartLightDto dto) {
     super(dto);
-    pin0 = newJunction(this, dto.getMinus(), P10, P50);
+    a = newJunction(this, dto.getB(), P10, P50);
-    pin1 = newJunction(this, dto.getPlus(), P90, P50);
+    b = newJunction(this, dto.getA(), P90, P50);
+    resistance = dto.getResistance();
     minVoltage = dto.getMinVoltage();
     maxVoltage = dto.getMaxVoltage();
     defect = dto.isDefect();
@@ -78,26 +75,20 @@ public class PartLight extends PartOther {
   }
 
   @Override
-  public void propagate(final Junction source) {
+  public void postCalculate() {
-    voltage = abs(pin1.getVoltage() - pin0.getVoltage());
+    potentialDifference = abs(b.getVoltage() - a.getVoltage());
-    if (voltage > maxVoltage) {
+    defect |= potentialDifference > maxVoltage;
-      defect = true;
+    if (defect || potentialDifference < minVoltage) {
-    }
+      color = BULB_OFF_COLOR;
-    if (defect) {
-      color = COLOR_DEFECT;
     } else {
-      final int v = (int) round(voltage / maxVoltage * 255);
+      final int c = (int) round(255 * potentialDifference / maxVoltage);
-      if (v < 10) {
+      color = new Color(c, c, 0);
-        color = BULB_OFF_COLOR;
-      } else {
-        color = new Color(v, v, 0);
-      }
     }
   }
 
   @Override
   protected void _render() {
-    render.line(pin0, pin1, Color.BLACK, SYMBOL_STROKE);
+    render.line(a, b, Color.BLACK, SYMBOL_STROKE);
     render.circle(new Position(P50, P50), BULB_RADIUS, Color.BLACK, SYMBOL_STROKE, color);
 
     final double diag = 0.33 * RASTER;
@@ -107,6 +98,7 @@ public class PartLight extends PartOther {
 
   @Override
   protected void _labels() {
+    final int x = RASTER / 2;
     final int y0;
     final int y1;
     if (getOrientation() == Orientation.R180) {
@@ -117,9 +109,9 @@ public class PartLight extends PartOther {
       y0 = P05;
       y1 = P95 - LABEL_FONT.getSize();
     }
-    render.textCenter(LABEL_FONT, "%.1fV (max)".formatted(maxVoltage), y0, Color.BLACK);
+    render.textCenter(LABEL_FONT, "%.1fV (max)".formatted(maxVoltage), x, y0, Color.BLACK);
     if (defect) {
-      render.textCenter(LABEL_FONT, "DEFEKT", y1, Color.RED);
+      render.textCenter(LABEL_FONT, "DEFEKT", x, y1, Color.RED);
     }
   }
 

src/main/java/de/ph87/electro/circuit/part/parts/PartLightDto.java

@@ -11,9 +11,11 @@ import lombok.ToString;
 @NoArgsConstructor
 public class PartLightDto extends PartDto {
 
-  private JunctionDto plus;
+  private JunctionDto a;
 
-  private JunctionDto minus;
+  private JunctionDto b;
+
+  private double resistance;
 
   private double minVoltage;
 
@@ -23,9 +25,10 @@ public class PartLightDto extends PartDto {
 
   public PartLightDto(final PartLight partLight) {
     super(partLight);
-    this.plus = new JunctionDto(partLight.getPin1());
+    this.a = new JunctionDto(partLight.getB());
-    this.minus = new JunctionDto(partLight.getPin0());
+    this.b = new JunctionDto(partLight.getA());
     this.defect = partLight.isDefect();
+    this.resistance = partLight.getResistance();
     this.minVoltage = partLight.getMinVoltage();
     this.maxVoltage = partLight.getMaxVoltage();
   }

src/main/java/de/ph87/electro/circuit/part/parts/PartSwitch1x1.java

@@ -1,8 +1,7 @@
 package de.ph87.electro.circuit.part.parts;
 
-import de.ph87.electro.circuit.ShortCircuit;
+import de.ph87.electro.circuit.part.InnerConnection;
 import de.ph87.electro.circuit.part.Junction;
-import de.ph87.electro.circuit.part.Orientation;
 import de.ph87.electro.circuit.part.PartOther;
 import de.ph87.electro.circuit.part.Position;
 import lombok.Getter;
@@ -10,6 +9,7 @@ import lombok.Setter;
 import lombok.ToString;
 
 import java.awt.*;
+import java.util.List;
 
 import static de.ph87.electro.CONFIG.*;
 
@@ -22,21 +22,16 @@ public class PartSwitch1x1 extends PartOther {
   private final Junction output;
 
   @Setter
-  private boolean state;
+  private boolean state = false;
 
   public PartSwitch1x1() {
     this(Position.ZERO);
   }
 
   public PartSwitch1x1(final Position position) {
-    this("Ausschalter", position, Orientation.R0, false);
+    super("Ausschalter", position);
-  }
+    common = newJunction(this, "C", P10, P50);
-
+    output = newJunction(this, "O", P90, P50);
-  public PartSwitch1x1(final String name, final Position position, final Orientation orientation, final boolean state) {
-    super(name, position, orientation);
-    common = newJunction(this, "", P10, P50);
-    output = newJunction(this, "", P90, P50);
-    this.state = state;
   }
 
   public PartSwitch1x1(final PartSwitch1x1Dto dto) {
@@ -51,19 +46,6 @@ public class PartSwitch1x1 extends PartOther {
     state = !state;
   }
 
-  @Override
-  public void propagate(final Junction source) throws ShortCircuit {
-    if (source == common) {
-      if (state) {
-        output.propagate(source.getVoltage());
-      }
-    } else if (source == output) {
-      if (state) {
-        common.propagate(source.getVoltage());
-      }
-    }
-  }
-
   @Override
   protected void _render() {
     if (!state) {
@@ -74,4 +56,12 @@ public class PartSwitch1x1 extends PartOther {
     }
   }
 
+  @Override
+  public List<InnerConnection> getInnerConnections() {
+    if (state) {
+      return List.of(new InnerConnection(common, output));
+    }
+    return super.getInnerConnections();
+  }
+
 }

src/main/java/de/ph87/electro/circuit/part/parts/PartSwitch1x2.java

@@ -1,14 +1,15 @@
 package de.ph87.electro.circuit.part.parts;
 
-import de.ph87.electro.circuit.ShortCircuit;
+import de.ph87.electro.circuit.part.InnerConnection;
 import de.ph87.electro.circuit.part.Junction;
-import de.ph87.electro.circuit.part.Orientation;
 import de.ph87.electro.circuit.part.PartOther;
 import de.ph87.electro.circuit.part.Position;
 import lombok.Getter;
 import lombok.Setter;
 import lombok.ToString;
 
+import java.util.List;
+
 import static de.ph87.electro.CONFIG.*;
 
 @Getter
@@ -22,22 +23,17 @@ public class PartSwitch1x2 extends PartOther {
   private final Junction output1;
 
   @Setter
-  private boolean state;
+  private boolean state = false;
 
   public PartSwitch1x2() {
     this(Position.ZERO);
   }
 
   public PartSwitch1x2(final Position position) {
-    this("Wechselschalter", position, Orientation.R0, false);
+    super("Wechselschalter", position);
-  }
+    common = newJunction(this, "C", P10, P50);
-
+    output0 = newJunction(this, "O0", P90, P25);
-  public PartSwitch1x2(final String name, final Position position, final Orientation orientation, final boolean state) {
+    output1 = newJunction(this, "O1", P90, P75);
-    super(name, position, orientation);
-    common = newJunction(this, "", P10, P50);
-    output0 = newJunction(this, "", P90, P25);
-    output1 = newJunction(this, "", P90, P75);
-    this.state = state;
   }
 
   public PartSwitch1x2(final PartSwitch1x2Dto dto) {
@@ -53,25 +49,6 @@ public class PartSwitch1x2 extends PartOther {
     state = !state;
   }
 
-  @Override
-  public void propagate(final Junction source) throws ShortCircuit {
-    if (source == common) {
-      if (state) {
-        output1.propagate(source.getVoltage());
-      } else {
-        output0.propagate(source.getVoltage());
-      }
-    } else if (source == output0) {
-      if (!state) {
-        common.propagate(source.getVoltage());
-      }
-    } else if (source == output1) {
-      if (state) {
-        common.propagate(source.getVoltage());
-      }
-    }
-  }
-
   @Override
   protected void _render() {
     if (!state) {
@@ -81,4 +58,12 @@ public class PartSwitch1x2 extends PartOther {
     }
   }
 
+  @Override
+  public List<InnerConnection> getInnerConnections() {
+    if (state) {
+      return List.of(new InnerConnection(common, output1));
+    }
+    return List.of(new InnerConnection(common, output0));
+  }
+
 }

src/main/java/de/ph87/electro/circuit/part/parts/PartSwitchCross.java

@@ -1,14 +1,15 @@
 package de.ph87.electro.circuit.part.parts;
 
-import de.ph87.electro.circuit.ShortCircuit;
+import de.ph87.electro.circuit.part.InnerConnection;
 import de.ph87.electro.circuit.part.Junction;
-import de.ph87.electro.circuit.part.Orientation;
 import de.ph87.electro.circuit.part.PartOther;
 import de.ph87.electro.circuit.part.Position;
 import lombok.Getter;
 import lombok.Setter;
 import lombok.ToString;
 
+import java.util.List;
+
 import static de.ph87.electro.CONFIG.*;
 
 @Getter
@@ -24,23 +25,18 @@ public class PartSwitchCross extends PartOther {
   private final Junction output1;
 
   @Setter
-  private boolean state;
+  private boolean state = false;
 
   public PartSwitchCross() {
     this(Position.ZERO);
   }
 
   public PartSwitchCross(final Position position) {
-    this("Kreuzschalter", position, Orientation.R0, false);
+    super("Kreuzschalter", position);
-  }
+    common0 = newJunction(this, "C0", P10, P25);
-
+    common1 = newJunction(this, "C1", P10, P75);
-  public PartSwitchCross(final String name, final Position position, final Orientation orientation, final boolean state) {
+    output0 = newJunction(this, "O0", P90, P25);
-    super(name, position, orientation);
+    output1 = newJunction(this, "O1", P90, P75);
-    common0 = newJunction(this, "", P10, P25);
-    common1 = newJunction(this, "", P10, P75);
-    output0 = newJunction(this, "", P90, P25);
-    output1 = newJunction(this, "", P90, P75);
-    this.state = state;
   }
 
   public PartSwitchCross(final PartSwitchCrossDto dto) {
@@ -57,35 +53,6 @@ public class PartSwitchCross extends PartOther {
     state = !state;
   }
 
-  @Override
-  public void propagate(final Junction source) throws ShortCircuit {
-    if (source == common0) {
-      if (state) {
-        output1.propagate(source.getVoltage());
-      } else {
-        output0.propagate(source.getVoltage());
-      }
-    } else if (source == common1) {
-      if (state) {
-        output0.propagate(source.getVoltage());
-      } else {
-        output1.propagate(source.getVoltage());
-      }
-    } else if (source == output0) {
-      if (state) {
-        common1.propagate(source.getVoltage());
-      } else {
-        common0.propagate(source.getVoltage());
-      }
-    } else if (source == output1) {
-      if (state) {
-        common0.propagate(source.getVoltage());
-      } else {
-        common1.propagate(source.getVoltage());
-      }
-    }
-  }
-
   @Override
   protected void _render() {
     if (!state) {
@@ -97,4 +64,18 @@ public class PartSwitchCross extends PartOther {
     }
   }
 
+  @Override
+  public List<InnerConnection> getInnerConnections() {
+    if (state) {
+      return List.of(
+        new InnerConnection(common0, output1),
+        new InnerConnection(common1, output0)
+      );
+    }
+    return List.of(
+      new InnerConnection(common0, output0),
+      new InnerConnection(common1, output1)
+    );
+  }
+
 }

src/test/java/de/ph87/electro/circuit/BatteryLightTest.java

@@ -12,27 +12,27 @@ public class BatteryLightTest {
 
   private static final double VOLTAGE = 3;
 
-  private static final Circuit circuit = new Circuit();
+  private static final Circuit CIRCUIT = new Circuit();
 
-  private static final PartBattery battery = circuit.addPart(new PartBattery());
+  private static final PartBattery battery = CIRCUIT.addPart(new PartBattery());
 
-  private static final PartLight light = circuit.addPart(new PartLight());
+  private static final PartLight light = CIRCUIT.addPart(new PartLight());
 
   @BeforeAll
   public static void setUp() {
-    circuit.connect(battery.getPlus(), light.getPin1());
+    CIRCUIT.connect(battery.getPlus(), light.getB());
-    circuit.connect(light.getPin0(), battery.getMinus());
+    CIRCUIT.connect(light.getA(), battery.getMinus());
   }
 
   @Test
   void test() {
-    circuit.evaluateAndRender();
+    CIRCUIT.evaluateAndRender();
 
     assertEquals(VOLTAGE, battery.getPlus().getVoltage());
-    assertEquals(VOLTAGE, light.getPin1().getVoltage());
+    assertEquals(VOLTAGE, light.getB().getVoltage());
-    assertEquals(VOLTAGE, light.getVoltage());
+    assertEquals(VOLTAGE, light.getPotentialDifference());
 
-    assertEquals(0, light.getPin0().getVoltage());
+    assertEquals(0, light.getA().getVoltage());
     assertEquals(0, battery.getMinus().getVoltage());
 
     assertFalse(light.isDefect());

src/test/java/de/ph87/electro/circuit/BatterySwitcher1x1Test.java

@@ -13,19 +13,19 @@ public class BatterySwitcher1x1Test {
 
   private static final double VOLTAGE = 3;
 
-  private static final Circuit circuit = new Circuit();
+  private static final Circuit CIRCUIT = new Circuit();
 
-  private static final PartBattery battery = circuit.addPart(new PartBattery());
+  private static final PartBattery battery = CIRCUIT.addPart(new PartBattery());
 
-  private static final PartSwitch1x1 switcher = circuit.addPart(new PartSwitch1x1());
+  private static final PartSwitch1x1 switcher = CIRCUIT.addPart(new PartSwitch1x1());
 
-  private static final PartLight light = circuit.addPart(new PartLight());
+  private static final PartLight light = CIRCUIT.addPart(new PartLight());
 
   @BeforeAll
   public static void setUp() {
-    circuit.connect(battery.getPlus(), switcher.getCommon());
+    CIRCUIT.connect(battery.getPlus(), switcher.getCommon());
-    circuit.connect(switcher.getOutput(), light.getPin1());
+    CIRCUIT.connect(switcher.getOutput(), light.getB());
-    circuit.connect(light.getPin0(), battery.getMinus());
+    CIRCUIT.connect(light.getA(), battery.getMinus());
   }
 
   @Test
@@ -43,7 +43,7 @@ public class BatterySwitcher1x1Test {
 
     switcher.setState(state);
 
-    circuit.evaluateAndRender();
+    CIRCUIT.evaluateAndRender();
 
     assertEquals(state, switcher.isState());
 
@@ -51,10 +51,10 @@ public class BatterySwitcher1x1Test {
     assertEquals(VOLTAGE, switcher.getCommon().getVoltage());
 
     assertEquals(voltage, switcher.getOutput().getVoltage());
-    assertEquals(voltage, light.getPin1().getVoltage());
+    assertEquals(voltage, light.getB().getVoltage());
-    assertEquals(voltage, light.getVoltage());
+    assertEquals(voltage, light.getPotentialDifference());
 
-    assertEquals(0, light.getPin0().getVoltage());
+    assertEquals(0, light.getA().getVoltage());
     assertEquals(0, battery.getMinus().getVoltage());
 
     assertFalse(light.isDefect());

src/test/java/de/ph87/electro/circuit/BatterySwitcher1x2Test.java

@@ -13,23 +13,23 @@ public class BatterySwitcher1x2Test {
 
   private static final double VOLTAGE = 3;
 
-  private static final Circuit circuit = new Circuit();
+  private static final Circuit CIRCUIT = new Circuit();
 
-  private static final PartBattery battery = circuit.addPart(new PartBattery());
+  private static final PartBattery battery = CIRCUIT.addPart(new PartBattery());
 
-  private static final PartSwitch1x2 switcher = circuit.addPart(new PartSwitch1x2());
+  private static final PartSwitch1x2 switcher = CIRCUIT.addPart(new PartSwitch1x2());
 
-  private static final PartLight light0 = circuit.addPart(new PartLight());
+  private static final PartLight light0 = CIRCUIT.addPart(new PartLight());
 
-  private static final PartLight light1 = circuit.addPart(new PartLight());
+  private static final PartLight light1 = CIRCUIT.addPart(new PartLight());
 
   @BeforeAll
   public static void setUp() {
-    circuit.connect(battery.getPlus(), switcher.getCommon());
+    CIRCUIT.connect(battery.getPlus(), switcher.getCommon());
-    circuit.connect(switcher.getOutput0(), light0.getPin1());
+    CIRCUIT.connect(switcher.getOutput0(), light0.getB());
-    circuit.connect(light0.getPin0(), battery.getMinus());
+    CIRCUIT.connect(light0.getA(), battery.getMinus());
-    circuit.connect(switcher.getOutput1(), light1.getPin1());
+    CIRCUIT.connect(switcher.getOutput1(), light1.getB());
-    circuit.connect(light1.getPin0(), battery.getMinus());
+    CIRCUIT.connect(light1.getA(), battery.getMinus());
   }
 
   @Test
@@ -48,7 +48,7 @@ public class BatterySwitcher1x2Test {
 
     switcher.setState(state);
 
-    circuit.evaluateAndRender();
+    CIRCUIT.evaluateAndRender();
 
     assertEquals(state, switcher.isState());
 
@@ -56,15 +56,15 @@ public class BatterySwitcher1x2Test {
     assertEquals(VOLTAGE, switcher.getCommon().getVoltage());
 
     assertEquals(voltage0, switcher.getOutput0().getVoltage());
-    assertEquals(voltage0, light0.getPin1().getVoltage());
+    assertEquals(voltage0, light0.getB().getVoltage());
-    assertEquals(voltage0, light0.getVoltage());
+    assertEquals(voltage0, light0.getPotentialDifference());
 
     assertEquals(voltage1, switcher.getOutput1().getVoltage());
-    assertEquals(voltage1, light1.getPin1().getVoltage());
+    assertEquals(voltage1, light1.getB().getVoltage());
-    assertEquals(voltage1, light1.getVoltage());
+    assertEquals(voltage1, light1.getPotentialDifference());
 
-    assertEquals(0, light0.getPin0().getVoltage());
+    assertEquals(0, light0.getA().getVoltage());
-    assertEquals(0, light1.getPin0().getVoltage());
+    assertEquals(0, light1.getA().getVoltage());
     assertEquals(0, battery.getMinus().getVoltage());
 
     assertFalse(light0.isDefect());

src/test/java/de/ph87/electro/circuit/BatterySwitcher2x2Test.java

@@ -13,23 +13,23 @@ public class BatterySwitcher2x2Test {
 
   private static final double VOLTAGE = 3;
 
-  private static final Circuit circuit = new Circuit();
+  private static final Circuit CIRCUIT = new Circuit();
 
-  private static final PartBattery battery = circuit.addPart(new PartBattery());
+  private static final PartBattery battery = CIRCUIT.addPart(new PartBattery());
 
-  private static final PartSwitch1x2 switcher0 = circuit.addPart(new PartSwitch1x2());
+  private static final PartSwitch1x2 switcher0 = CIRCUIT.addPart(new PartSwitch1x2());
 
-  private static final PartSwitch1x2 switcher1 = circuit.addPart(new PartSwitch1x2());
+  private static final PartSwitch1x2 switcher1 = CIRCUIT.addPart(new PartSwitch1x2());
 
-  private static final PartLight light = circuit.addPart(new PartLight());
+  private static final PartLight light = CIRCUIT.addPart(new PartLight());
 
   @BeforeAll
   public static void setUp() {
-    circuit.connect(battery.getPlus(), switcher0.getCommon());
+    CIRCUIT.connect(battery.getPlus(), switcher0.getCommon());
-    circuit.connect(switcher0.getOutput0(), switcher1.getOutput0());
+    CIRCUIT.connect(switcher0.getOutput0(), switcher1.getOutput0());
-    circuit.connect(switcher0.getOutput1(), switcher1.getOutput1());
+    CIRCUIT.connect(switcher0.getOutput1(), switcher1.getOutput1());
-    circuit.connect(switcher1.getCommon(), light.getPin1());
+    CIRCUIT.connect(switcher1.getCommon(), light.getB());
-    circuit.connect(light.getPin0(), battery.getMinus());
+    CIRCUIT.connect(light.getA(), battery.getMinus());
   }
 
   @Test
@@ -60,7 +60,7 @@ public class BatterySwitcher2x2Test {
     switcher0.setState(state0);
     switcher1.setState(state1);
 
-    circuit.evaluateAndRender();
+    CIRCUIT.evaluateAndRender();
 
     assertEquals(state0, switcher0.isState());
     assertEquals(state1, switcher1.isState());
@@ -75,10 +75,10 @@ public class BatterySwitcher2x2Test {
     assertEquals(voltage1, switcher1.getOutput1().getVoltage());
 
     assertEquals(voltage, switcher1.getCommon().getVoltage());
-    assertEquals(voltage, light.getPin1().getVoltage());
+    assertEquals(voltage, light.getB().getVoltage());
-    assertEquals(voltage, light.getVoltage());
+    assertEquals(voltage, light.getPotentialDifference());
 
-    assertEquals(0, light.getPin0().getVoltage());
+    assertEquals(0, light.getA().getVoltage());
     assertEquals(0, battery.getMinus().getVoltage());
 
     assertFalse(light.isDefect());

src/test/java/de/ph87/electro/circuit/BatterySwitcherCrossTest.java

@@ -14,27 +14,27 @@ public class BatterySwitcherCrossTest {
 
   private static final double VOLTAGE = 3;
 
-  private static final Circuit circuit = new Circuit();
+  private static final Circuit CIRCUIT = new Circuit();
 
-  private static final PartBattery battery = circuit.addPart(new PartBattery());
+  private static final PartBattery battery = CIRCUIT.addPart(new PartBattery());
 
-  private static final PartSwitch1x2 switcher0 = circuit.addPart(new PartSwitch1x2());
+  private static final PartSwitch1x2 switcher0 = CIRCUIT.addPart(new PartSwitch1x2());
 
-  private static final PartSwitchCross switcherX = circuit.addPart(new PartSwitchCross());
+  private static final PartSwitchCross switcherX = CIRCUIT.addPart(new PartSwitchCross());
 
-  private static final PartSwitch1x2 switcher1 = circuit.addPart(new PartSwitch1x2());
+  private static final PartSwitch1x2 switcher1 = CIRCUIT.addPart(new PartSwitch1x2());
 
-  private static final PartLight light = circuit.addPart(new PartLight());
+  private static final PartLight light = CIRCUIT.addPart(new PartLight());
 
   @BeforeAll
   public static void setUp() {
-    circuit.connect(battery.getPlus(), switcher0.getCommon());
+    CIRCUIT.connect(battery.getPlus(), switcher0.getCommon());
-    circuit.connect(switcher0.getOutput0(), switcherX.getCommon0());
+    CIRCUIT.connect(switcher0.getOutput0(), switcherX.getCommon0());
-    circuit.connect(switcher0.getOutput1(), switcherX.getCommon1());
+    CIRCUIT.connect(switcher0.getOutput1(), switcherX.getCommon1());
-    circuit.connect(switcherX.getOutput0(), switcher1.getOutput0());
+    CIRCUIT.connect(switcherX.getOutput0(), switcher1.getOutput0());
-    circuit.connect(switcherX.getOutput1(), switcher1.getOutput1());
+    CIRCUIT.connect(switcherX.getOutput1(), switcher1.getOutput1());
-    circuit.connect(switcher1.getCommon(), light.getPin1());
+    CIRCUIT.connect(switcher1.getCommon(), light.getB());
-    circuit.connect(light.getPin0(), battery.getMinus());
+    CIRCUIT.connect(light.getA(), battery.getMinus());
   }
 
   @Test
@@ -88,7 +88,7 @@ public class BatterySwitcherCrossTest {
     switcherX.setState(stateX);
     switcher1.setState(state1);
 
-    circuit.evaluateAndRender();
+    CIRCUIT.evaluateAndRender();
 
     assertEquals(state0, switcher0.isState());
     assertEquals(stateX, switcherX.isState());
@@ -110,10 +110,10 @@ public class BatterySwitcherCrossTest {
     assertEquals(voltageX1, switcher1.getOutput1().getVoltage());
 
     assertEquals(voltage, switcher1.getCommon().getVoltage());
-    assertEquals(voltage, light.getPin1().getVoltage());
+    assertEquals(voltage, light.getB().getVoltage());
-    assertEquals(voltage, light.getVoltage());
+    assertEquals(voltage, light.getPotentialDifference());
 
-    assertEquals(0, light.getPin0().getVoltage());
+    assertEquals(0, light.getA().getVoltage());
     assertEquals(0, battery.getMinus().getVoltage());
 
     assertFalse(light.isDefect());

src/test/java/de/ph87/electro/circuit/CircuitCalculationServiceTest.java

@@ -13,15 +13,15 @@ import java.nio.charset.StandardCharsets;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-class CircuitServiceTest {
+class CircuitCalculationServiceTest {
 
   @Test
   void serialization() throws IOException {
     final Circuit circuit = new Circuit();
     final PartBattery battery = circuit.addPart(new PartBattery());
     final PartLight light = circuit.addPart(new PartLight());
-    circuit.connect(battery.getPlus(), light.getPin1());
+    circuit.connect(battery.getPlus(), light.getB());
-    circuit.connect(light.getPin0(), battery.getMinus());
+    circuit.connect(light.getA(), battery.getMinus());
     check(circuit);
   }
 

src/test/java/de/ph87/electro/circuit/net/CalculationServiceTest.java

@@ -0,0 +1,40 @@
+package de.ph87.electro.circuit.net;
+
+import de.ph87.electro.circuit.Calculation;
+import de.ph87.electro.circuit.Circuit;
+import de.ph87.electro.circuit.Wire;
+import de.ph87.electro.circuit.part.Junction;
+import de.ph87.electro.circuit.part.parts.PartBattery;
+import de.ph87.electro.circuit.part.parts.PartLight;
+import lombok.extern.slf4j.Slf4j;
+import org.junit.jupiter.api.Test;
+
+@Slf4j
+class CalculationServiceTest {
+
+  @Test
+  void test() {
+    final Circuit circuit = new Circuit();
+    final PartBattery battery = circuit.addPart(new PartBattery());
+    final PartLight light = circuit.addPart(new PartLight());
+    circuit.connect(battery.getMinus(), light.getA());
+    circuit.connect(battery.getPlus(), light.getB());
+
+    final Calculation calculation = new Calculation(circuit);
+
+    calculation.toString().lines().forEach(log::info);
+    circuit.streamParts().forEach(part -> {
+      log.info("");
+      log.info(part.toString());
+      for (final Junction junction : part.getJunctions()) {
+        log.info("  \"%s\" = %.2f V".formatted(junction.getName(), junction.getVoltage()));
+        for (final Wire wire : junction.getWires()) {
+          final Junction opposite = wire.getOpposite(junction);
+          log.info("    -> %s.%s = %.2f A".formatted(opposite.getOwner().getName(), opposite.getName(), wire.getCurrent(junction)));
+        }
+      }
+    });
+    log.info("");
+  }
+
+}

src/test/java/de/ph87/electro/circuit/net/CalculationTest.java

@@ -0,0 +1,19 @@
+package de.ph87.electro.circuit.net;
+
+import de.ph87.electro.circuit.Calculation;
+import lombok.extern.slf4j.Slf4j;
+import org.junit.jupiter.api.Test;
+
+@Slf4j
+class CalculationTest {
+
+  @Test
+  void test() {
+    final Calculation calculation = new Calculation(1);
+    calculation.addResistor(-1, 0, 15);
+    calculation.addCurrentSource(-1, 0, 4, 5);
+    calculation.solve();
+    calculation.toString().lines().forEach(log::info);
+  }
+
+}