public void update() {
    stressBeforeUpdate = stressAfterUpdate;

    computeBofCoordinates();
    BZ.multiply(newPositionMatrix, positionMatrix);
    positionMatrix.set(newPositionMatrix);
    vPlus.substituteBack(positionMatrix);
    distances.set(new DistanceMatrix(positions));
    stressAfterUpdate = stress();

    iterations++;
  }