Dear all,

I have spent some time trying to figure out my problem, but haven't succeeded so I am posting here.

Since I thought about OpenCL for the first time, I thought it would be great to implement method of lines for solving PDE equation. So I started from the very basic example - 1D hyperbolic equation (simple string oscillations).

Starting from initialization:
Code :
int fixed=1;
    for (i = 0; i < loops; i++)
	{
	  u[0][i] = fixed;
	  u[1][i] = fixed;
	  u[2][i] = fixed;
 
	  u[n-1][i] = fixed;
	  u[n-2][i] = fixed;
	  u[n-3][i] = fixed;
 
	  y[0] = 0.0;
	  y[n-1] = 0.0;
	}
 
    for (i = 0; i < n; i++)
	{
    u[i][0] = fosc (i2x (i));
    u[i][1] = fosc (i2x (i)); 
    u[i][2] = fosc (i2x (i));  
	input[i] = u[i][2];
	y[i] = (u[i][2] - u[i][0])/2.0/dt;
	}

Where function fosc gives me simple Sine function profile from -50 to 50.
Code :
float
fosc (float x)
{
  float osc;
 osc=1+sin(x*3.1415926/100+3.1415926/2.0);                         //simple string
  return osc;
}

I have created following buffers for input, output and derivatives:

Code :
cl_mem inputBuffer = clCreateBuffer(context, CL_MEM_READ_WRITE|CL_MEM_COPY_HOST_PTR, n * sizeof(float),(void *) input, NULL);
	cl_mem outputBuffer = clCreateBuffer(context, CL_MEM_READ_WRITE , n*loops * sizeof(float), NULL, NULL);
	cl_mem devs = clCreateBuffer(context, CL_MEM_READ_WRITE|CL_MEM_COPY_HOST_PTR, n * sizeof(float),(void *)y, NULL);

Since it is not valid to pass 2D arrays in kernel, I slice the output function with indexing
[x+SizeX*y]

Code :
	for (j=0; j<loops; j++){	  
	  for (i=0; i<n; i++){
	    u[i][j+2]=output[i+n*j];
	    if (i%(n/8) == 0) {
	    cout << u[i][j] << "    ";
	  }
	  }
	 cout<<endl; 
	}


Then I came up with the following kernel:

Code :
float
an (float fn2, float fn1, float fn, float fn11, float fn22, float dh)
{
  return (-fn2 + 16.0 * fn1 - 30.0 * fn + 16.0 * fn11 - fn22) / 12.0 / dh / dh - func (fn);	//4-th space order second derivative
}
 
 
__kernel void helloworld(__global float* in, __global float* out, int n, int loops, __global float* devs)
{
	int t;	
	float dh=100.0/n;
	float dt=100.0/loops;
 
	int i = get_global_id(0);
	float y[1000];
	float u[1000];
 
	float k1[1000];float k2[1000];float k3[1000];float k4[1000];
	float m1[1000];	float m2[1000];	float m3[1000];	float m4[1000];
 
if ( (i>-1) &&  (i<n) ) {
u[i]=in[i];	//receiving initial field values
y[i]=devs[i];  //receiving initial derivatives
		}
 
for (t=0; t < loops; t++) {
 
if ( (i>1) &&  (i<n-2) ) {
 
      k1[i] =
	an (u[i - 2], u[i - 1], u[i], u[i + 1], u[i + 2], dh) * dt;
      m1[i] = y[i] * dt;
 
      k2[i] =
	an (u[i - 2] + m1[i - 2] / 2.0,
	    u[i - 1] + m1[i - 1] / 2.0, u[i] + m1[i] / 2.0,
	    u[i + 1] + m1[i + 1] / 2.0,
	    u[i + 2] + m1[i + 2] / 2.0, dh) * dt;
      m2[i] = (y[i] + k1[i] / 2.0) * dt;
 
      k3[i] =
	an (u[i - 2] + m2[i - 2] / 2.0,
	    u[i - 1] + m2[i - 1] / 2.0, u[i] + m2[i] / 2.0,
	    u[i + 1] + m2[i + 1] / 2.0,
	    u[i + 2] + m2[i + 2] / 2.0, dh) * dt;
      m3[i] = (y[i] + k2[i] / 2.0) * dt;
 
      k4[i] =
	an (u[i - 2] + m3[i - 2], u[i - 1] + m3[i - 1],
	    u[i] + m3[i], u[i + 1] + m3[i + 1],
	    u[i + 2] + m3[i + 2], dh) * dt;
      m4[i] = (y[i] + k3[i]) * dt;
 
y[i] = y[i] + (k1[i] + 2.0 * k2[i] + 2.0 * k3[i] + k4[i]) / 6.0;
u[i] = u[i] + (m1[i] + 2.0 * m2[i] + 2.0 * m3[i] + m4[i]) / 6.0;
 
out[i+n*t] = u[i];
 
} else {
out[i+n*t] = 1;   }
}
 
}


Now the problem is that the code is working in usual C++ program but when I moved to OpenCL it doesn't. Instead of harmonic oscillations, I can see random numbers popping up here and there.

The algorithm looks fine to me, I can not figure out the problem.
I would appreciate any help.