About dgetf2_nopiv_device. Why m is passed but not used.

[Aran Nokan]

Hi,

I have question about the dgetf2_nopiv_device kernel. Why m has been passed but not used. How is it working without m?

The code also pasted here: https://paste.debian.net/1260203/

// This kernel uses registers for matrix storage, shared mem. for communication.
// It also uses lazy swap.
//extern __shared__ double zdata[];

template<int N>
__device__ void
dgetf2_nopiv_device(int m, double* dA, int ldda, magma_int_t *info, const int tx, double* sx, int gbstep)
{
    double rA[N] = {MAGMA_D_ZERO};
    double reg = MAGMA_D_ZERO;
   
    int linfo = 0;
    double abs;
    // check from previous calls if the panel factorization failed previously
    // this is necessary to report the correct info value
    if(gbstep > 0 && *info != 0) return;

    // read
    #pragma unroll
    for(int i = 0; i < N; i++){
        rA[i] = dA[ i * ldda + tx ];
    }
       
    #pragma unroll
    for(int i = 0; i < N; i++){
        if(tx == i){
            #pragma unroll
            for(int j = 0; j < N; j++)
                sx[j] = rA[j];
        }
        __syncthreads();

        abs = fabs(MAGMA_D_REAL( sx[i] )) + fabs(MAGMA_D_IMAG( sx[i] ));
        linfo = ( abs == MAGMA_D_ZERO && linfo == 0) ? (gbstep+i+1) : linfo;
        //linfo = ( abs  == MAGMA_D_ZERO ) ? min(linfo,gbstep+i+1):0;
        reg   = (linfo == 0 ) ? MAGMA_D_DIV(MAGMA_D_ONE, sx[i] ) : MAGMA_D_ONE;

        // scal and ger
        if( tx > i ){
            rA[i] *= reg;
            #pragma unroll
            for(int j = i+1; j < N; j++){
                rA[j] -= rA[i] * sx[j];
            }
        }
        __syncthreads();
    }

    if(tx == 0){
        (*info) = (magma_int_t)( linfo );
    }

    // write
    #pragma unroll
    for(int i = 0; i < N; i++){
        dA[ i * ldda + tx ] = rA[i];
    }
}

Best regards,

A. N.

[Ahmad Abdelfattah]

If it is not appearing in the code, then perhaps it shouldn’t be passed. The ‘nopiv’ name indicates that there is no search for the pivot (during which you will need ‘m’). 

Ahmad

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