Discrete Laplace Operator in Java (Matlab del2 in Java) [TESTED]

del2_java

 /*
 * ----------------------------------------------------------------------------
 * "THE BEER-WARE LICENSE" (Revision 42):
 * As long as you retain this notice you
 * can do whatever you want with this stuff. If we meet some day, and you think
 * this stuff is worth it, you can buy me a beer.
 * ----------------------------------------------------------------------------
 */
 
  // Compute Discrete laplacian Operator of U and V
  // Is matlab del2 function in Java
  // It was tested with matlab side-by-side
    
  // * You can put a wrap around loop to da iteractive diffusion
  
  // iterative diffusion (optional)
	//	for(int loop=0;loop<ITER;loop++) {
    

      // Interior
			for (int x=1 ; x < w-1 ; x++){
				for (int y=1 ; y < h-1 ; y++) {
					
					if(x > 0 && y > 0 && x < w-1 && y < h-1){
						Lu[x][y] = ((u[x-1][y]+u[x+1][y] + u[x][y-1] + u[x][y+1]) - 4 * u[x][y]) / 4; 
						Lv[x][y] = ((v[x-1][y]+v[x+1][y] + v[x][y-1] + v[x][y+1]) - 4 * v[x][y]) / 4;
					}				
				}
			}
			
			// Sides
			for (int x=0 ; x < w ; x++) {
				for (int y=0 ; y < h ; y++) {

					if(x > 0 && y > 0 && x < w-1 && y < h-1){
					}else{
						if(x==0 && y ==0){
						}
						else if(y == 0 && x < w-1){
							Lu[x][y] = (-5 * u[x][y+1] + 4 * u[x][y+2] - u[x][y+3] + 2 * u[x][y] + u[x+1][y] + u[x-1][y] - 2 * u[x][y]) / 4;
							Lv[x][y] = (-5 * v[x][y+1] + 4 * v[x][y+2] - v[x][y+3] + 2 * v[x][y] + v[x+1][y] + v[x-1][y] - 2 * v[x][y]) / 4;
						}
						
						else if(x == 0  && y < h-1){
							Lu[x][y] = (-5 * u[x+1][y] + 4 * u[x+2][y] - u[x+3][y] + 2 * u[x][y] + u[x][y+1] + u[x][y-1] - 2 * u[x][y]) / 4;
							Lv[x][y] = (-5 * v[x+1][y] + 4 * v[x+2][y] - v[x+3][y] + 2 * v[x][y] + v[x][y+1] + v[x][y-1] - 2 * v[x][y]) / 4;
						}
						
						else if(y == h-1 && x > 0 && x < w-1){
							Lu[x][y] = (-5 * u[x][y-1] + 4 * u[x][y-2] - u[x][y-3] + 2 * u[x][y] + u[x+1][y] + u[x-1][y] - 2 * u[x][y]) / 4;
							Lv[x][y] = (-5 * v[x][y-1] + 4 * v[x][y-2] - v[x][y-3] + 2 * v[x][y] + v[x+1][y] + v[x-1][y] - 2 * v[x][y]) / 4;
						}
						
						else if(x == w-1 && y > 0 && y < h-1){
							Lu[x][y] = (-5 * u[x-1][y] + 4 * u[x-2][y] - u[x-3][y] + 2 * u[x][y] + u[x][y+1] + u[x][y-1] - 2 * u[x][y]) / 4;
							Lv[x][y] = (-5 * v[x-1][y] + 4 * v[x-2][y] - v[x-3][y] + 2 * v[x][y] + v[x][y+1] + v[x][y-1] - 2 * v[x][y]) / 4;
						}
					}
				}
			}
			
			// Corners
			
			//ul
			int x = 0;
			int y = 0;
			Lu[x][y] = (-5 * u[x][y+1] + 4 * u[x][y+2] - u[x][y+3] + 2 * u[x][y] - 5 * u[x+1][y] + 4 * u[x+2][y] - u[x+3][y] + 2 * u[x][y]) / 4;
			Lv[x][y] = (-5 * v[x][y+1] + 4 * v[x][y+2] - v[x][y+3] + 2 * v[x][y] - 5 * v[x+1][y] + 4 * v[x+2][y] - v[x+3][y] + 2 * v[x][y]) / 4;
			
			//br
			x = w-1;
			y = h-1;
			Lu[x][y] = (-5 * u[x][y-1] + 4 * u[x][y-2] - u[x][y-3] + 2 * u[x][y] - 5 * u[x-1][y] + 4 * u[x-2][y] - u[x-3][y] + 2 * u[x][y]) / 4;
			Lv[x][y] = (-5 * v[x][y-1] + 4 * v[x][y-2] - v[x][y-3] + 2 * v[x][y] - 5 * v[x-1][y] + 4 * v[x-2][y] - v[x-3][y] + 2 * v[x][y]) / 4;
				
			//bl
			x = 0;
			y = h-1;
			Lu[x][y] = (-5 * u[x][y-1] + 4 * u[x][y-2] - u[x][y-3] + 2 * u[x][y] - 5 * u[x+1][y] + 4 * u[x+2][y] - u[x+3][y] + 2 * u[x][y]) / 4;
			Lv[x][y] = (-5 * v[x][y-1] + 4 * v[x][y-2] - v[x][y-3] + 2 * v[x][y] - 5 * v[x+1][y] + 4 * v[x+2][y] - v[x+3][y] + 2 * v[x][y]) / 4;
			
			//ur
			x = w-1;
			y = 0;
			Lu[x][y] = (-5 * u[x][y+1] + 4 * u[x][y+2] - u[x][y+3] + 2 * u[x][y] - 5 * u[x-1][y] + 4 * u[x-2][y] - u[x-3][y] + 2 * u[x][y]) / 4;
			Lv[x][y] = (-5 * v[x][y+1] + 4 * v[x][y+2] - v[x][y+3] + 2 * v[x][y] - 5 * v[x-1][y] + 4 * v[x-2][y] - v[x-3][y] + 2 * v[x][y]) / 4;
			
	//	} // loop diffusion - (optional)

This help me a lot, thank you!