OpenCL - incremental summation during compute
- by user1721997
I'm absolutelly novice in OpenCL programming. For my app. (molecular simulaton) I wrote a kernel for calculate intermolecular potential of lennard-jones liquid. In this kernel I need to compute cumulative value of the potential of all particles with one:
__kernel void Molsim(__global const float* inmatrix, __global float* fi, const int c, const float r1, const float r2, const float r3, const float rc, const float epsilon, const float sigma, const float h1, const float h23)
{
float fi0;
float fi1;
float d;
unsigned int i = get_global_id(0); //number of particles (typically 2000)
if(c!=i) {
// potential before particle movement
d=sqrt(pow((0.5*h1-fabs(0.5*h1-fabs(inmatrix[c*3]-inmatrix[i*3]))),2.0)+pow((0.5*h23-fabs(0.5*h23-fabs(inmatrix[c*3+1]-inmatrix[i*3+1]))),2.0)+pow((0.5*h23-fabs(0.5*h23-fabs(inmatrix[c*3+2]-inmatrix[i*3+2]))),2.0));
if(d<rc) {
fi0=4.0*epsilon*(pow(sigma/d,12.0)-pow(sigma/d,6.0));
}
else {
fi0=0;
}
// potential after particle movement
d=sqrt(pow((0.5*h1-fabs(0.5*h1-fabs(r1-inmatrix[i*3]))),2.0)+pow((0.5*h23-fabs(0.5*h23-fabs(r2-inmatrix[i*3+1]))),2.0)+pow((0.5*h23-fabs(0.5*h23-fabs(r3-inmatrix[i*3+2]))),2.0));
if(d<rc) {
fi1=4.0*epsilon*(pow(sigma/d,12.0)-pow(sigma/d,6.0));
}
else {
fi1=0;
}
// cumulative difference of potentials
fi[0]+=fi1-fi0;
}
}
My problem is in the line: fi[0]+=fi1-fi0;. In the one-element vector fi[0] are wrong results.
I read something about sum reduction, but I do not know how to do it during the calculation.
Exist any simple solution of my problem?
