Question

I have following kernel code for matrix manipulation. Matrix A = 1*3 and Matrix B = 3*3 resultant Matrix C would be 1*3. In the following code the width would be 3.

__global__void MatrixMulKernel(float* d_M,float* d_N,float* d_P,int Width) {
   int row = blockIdx.y * blockDim.y + threadIdx.y;
   int col = blockIdx.x * blockDim.x + threadIdx.x;
    if(row>=Width || col>=Width){  // matrix range
      return;
    }
   float P_val = 0.0f;
   for (int k = 0; k < Width; ++k) {
   float M_elem = d_M[row * Width + k];
   float N_elem = d_N[k * Width + col];
   P_val += M_elem * N_elem;
  }
 d_p[row*Width+col] = P_val;
}

I kernel code is called as follows

int block_size = 32;
dim3 dimGrid(Width/block_size, Width/block_size);
dim3 dimBlock(block_size, block size);
MatrixMulKernel<<<dimGrid, dimBlock>>>(d_M, d_N, d_P,3);

But I am getting wrong results. I am getting results as zero always.
Can anyone help me please.

Answer 1

The code looks likes its for multiplication of 2 square matrices of same size.

Width is the number of columns of the first matrix.

You have to provide this as an argument to the function.