Using matrix multiplication in processingjs for an attractor

matrix.pde

// matrix.pde
// Using matrix multiplication in processingjs for an attractor

void setup() {
  size(250,250);
  frameRate(20);
  strokeWeight(2);
  translate(125,125);
  text("click mouse", 0, 0);
  text(matrixA, -100, 20);
}

void mousePressed() {
  background(50);
  //line(random(width),random(height),random(width),random(height));


  pushMatrix();
  translate(125,125);

  // center line
  stroke(255,156,0);
  strokeWeight(1);
  line(-4, 0, 4, 0);
  line(0, -4, 0, 4);

  stroke(0,156,255);
  strokeWeight(2);

  line(matrixC[0][0],matrixC[0][1],matrixC[1][0],matrixC[1][1]);
  text(matrixA, 0,70); // width/2,height/2);
  multiply(matrixA,matrixB,matrixC); // C = A*B
  //text(matrixA, 0,60); 
  //arrayCopy(matrixC,matrixA); 
  //arrayCopy(matrixC,matrixA); // A = C
  //matrixC = matrixA.reverse().reverse();
  multiply(matrixC,matrixId,matrixA); // A = C*Id = C
  text(matrixC, 0,90); 
  popMatrix();
}

int[][] matrixId = {{1,0},{0,1}};
int[][] matrixA = {{round(random(width)/2),round(random(height)/2)},{round(random(width)/2),random(height)/2}};
int[][] matrixB= {{0,-0.9},{1.0,0}};
int[][] matrixC = {{0,0},{0,0}}; // new int[2][2];


void multiply(matrixA,matrixB,matrixC)
{

  
  for(int i=0; i<2; i++){
           for(int j=0; j<2; j++){
               matrixC[i][j] = 0;
               for(int k=0; k<2; k++){               
               
                 matrixC[i][j]= matrixC[i][j]+ matrixA[i][k] * matrixB[k][j];
              
               }
               matrixC[i][j] = round(matrixC[i][j]*100)/100;
           }
       }
}