Finding the min value of a row in a 2d array

Hi all, still quite new to CUDA. As the title says i’m looking for a way to find the min value in a 2d array. Using the reduction method in the SDK Browser, i’ve managed to get it working for the first row, I just don’t know the right way to build up the algorithm to support finding the value over many rows.

My kernel is as follows:

__global__ void test_ker(float *b, float *o, int n) {

	__shared__ int  value[32];// allocated on invocation

	// perform first level of reduction,

	// reading from global memory, writing to shared memory

	unsigned int tid = threadIdx.x;

	unsigned int i = blockIdx.x*(blockDim.x*2) + threadIdx.x;

	value[tid] = fminf(b[i], b[i+blockDim.x]);


	// do reduction in shared mem

	for(unsigned int s=blockDim.x/2; s>0; s>>=1) 


		if (tid < s) 


	value[tid] = fminf(value[tid], value[tid+s]);




	// write result for this block to global mem 

	if (tid == 0) o[blockIdx.x] = value[0];


Any help would be very apreciated on this topic. Many thanks in advance!

You are now using a 1D grid. You can use a 2D grid, and use blockIdx.y as row-index, to find all values in one go. You just need to adjust the indexing to also take blockIdx.y into account (both in reading the source array as in writing the output array)