DufortFrankel.java

float FNext[][] = new float[F.length][F[0].length];
float r = deltaT*diffusionRate/deltaXSq;
for(int i=0;i<F.length;++i) {
  for(int j=0;j<F[0].length;++j) {
    //get the neighboring values with boundary conditions
    float iPrev, iNext, jNext, jPrev;
    if(i==0) iPrev = F[i][j];
    else iPrev = F[i-1][j];
    if(i==F.length-1) iNext = F[i][j];
    else iNext = F[i+1][j];
    if(j==0) jPrev = F[i][j];
    else jPrev = F[i][j-1];
    if(j==F[0].length-1) jNext = F[i][j];
    else jNext = F[i][j+1];
    //Dufort-Frankel step
    FNext[i][j] = (1-2*r)/(1+2*r)*(FPrev[i][j])+r/(1+2*r)*(iPrev+iNext+jPrev+jNext);
  }
}
FPrev = F;
F = FNext;