core_slarfx_tbrd.c

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#include <lapacke.h>
#include "common.h"

/***************************************************************************/
int 
CORE_slarfx2(PLASMA_enum side, int N,
             float V,
             float TAU,
             float *C1, int LDC1,
             float *C2, int LDC2)
{
    float V2, T2, SUM;
    int j;

    if (TAU == (float)0.0)
        return PLASMA_SUCCESS;

    /*
     * Special code for 2 x 2 Householder where V1 = I
    */
    if(side==PlasmaLeft){
        V2 = (V);
        T2 = TAU*(V2);
        for (j = 0; j < N ; j++, C1+=LDC1 ) {
            SUM = *C1 + V2 * (*C2);
            *C1 = *C1 - SUM*TAU;
            *C2 = *C2 - SUM*T2;
            C2 += LDC2;
        }
    }
    else {
        V2 = V;
        T2 = TAU*(V2);
        for (j = 0; j < N ; j++, C1++){
            SUM = *C1 + V2 * (*C2);
            *C1 = *C1 - SUM*TAU;
            *C2 = *C2 - SUM*T2;
            C2++;
        }
    }

    return PLASMA_SUCCESS;
}


/***************************************************************************/
int 
CORE_slarfx2c(PLASMA_enum uplo,
              float V,
              float TAU,
              float *C1,
              float *C2,
              float *C3)
{
    float T2, SUM, TEMP;

    /* Quick return */
    if (TAU == (float)0.0)
        return PLASMA_SUCCESS;

    /*
     *        Special code for a diagonal block  C1
     *                                           C2  C3
     */
    if(uplo==PlasmaLower) {   
        /* 
         *  Do the corner Left then Right (used for the lower case
         *  tridiag) L and R for the 2x2 corner
         *             C(N-1, N-1)  C(N-1,N)        C1  TEMP 
         *             C(N  , N-1)  C(N  ,N)        C2  C3 
         *  For Left : use (TAU) and V. 
         *  For Right: nothing, keep TAU and V. 
         *  Left 1 ==> C1 
         *             C2 
         */
        TEMP = (*C2); /*  copy C2 here before modifying it. */
        T2   = (TAU) * V;
        SUM  = *C1 + (V) * (*C2);
        *C1  = *C1 - SUM * (TAU);
        *C2  = *C2 - SUM * T2;
        /*  Left 2 ==> TEMP */
        /*             C3 */
        SUM  = TEMP + (V) * (*C3);
        TEMP = TEMP - SUM * (TAU);
        *C3  = *C3  - SUM * T2;
        /*  Right 1 ==>  C1 TEMP.  NB: no need to compute corner (2,2)=TEMP */
        T2  = TAU * (V);
        SUM = *C1 + V*TEMP;
        *C1 = *C1 - SUM*TAU;
        /*  Right 2 ==> C2 C3 */
        SUM = *C2   + V*(*C3);
        *C2 = *C2   - SUM*TAU;
        *C3 = *C3   - SUM*T2;
    }
    else { 
        /*  
         * Do the corner Right then Left (used for the upper case tridiag) 
         *             C(N-1, N-1)  C(N-1,N)        C1    C2 
         *             C(N  , N-1)  C(N  ,N)        TEMP  C3 
         *  For Left : use TAU       and (V). 
         *  For Right: use (TAU) and (V). 
         *  Right 1 ==> C1 C2 
         */
        V    = (V);
        TEMP = (*C2); /*  copy C2 here before modifying it. */
        T2   = (TAU) * (V);
        SUM  = *C1 + V   * (*C2);
        *C1  = *C1 - SUM * (TAU);
        *C2  = *C2 - SUM * T2;
        /*  Right 2 ==> TEMP C3 */
        SUM  = TEMP + V   * (*C3);
        TEMP = TEMP - SUM * (TAU);
        *C3  = *C3  - SUM * T2;
        /*  Left 1 ==> C1 */
        /*             TEMP. NB: no need to compute corner (2,1)=TEMP */
        T2  = TAU * V;
        SUM = *C1 + (V) * TEMP;
        *C1 = *C1 - SUM * TAU;
        /*  Left 2 ==> C2 */
        /*             C3 */
        SUM = *C2 + (V) * (*C3);
        *C2 = *C2 - SUM * TAU;
        *C3 = *C3 - SUM * T2;
    }

    return PLASMA_SUCCESS;
}


/***************************************************************************/
int 
CORE_slarfx2ce(PLASMA_enum uplo,
               float *V,
               float *TAU,
               float *C1,
               float *C2,
               float *C3)
{
    float T2, SUM, TEMP, VIN, TAUIN;

    /* Quick return */
    if (*TAU == (float)0.0)
        return PLASMA_SUCCESS;

    /*
     *        Special code for a diagonal block  C1
     *                                           C2  C3
     */
    if(uplo==PlasmaLower){    
        /*
         *  Do the corner for the lower case BIDIAG ==> Left then will
         *  create a new nnz. eliminate it and modify V TAU and then
         *  Right L and R for the 2x2 corner
         *             C(N-1, N-1)  C(N-1,N)        C1  TEMP 
         *             C(N  , N-1)  C(N  ,N)        C2  C3 
         */
        VIN   = *V;
        TAUIN = (*TAU);
        /*  Left 1 ==> C1 */
        /*             C2 */
        VIN  = (VIN);
        T2   = TAUIN * (VIN);
        SUM  = *C1   + VIN*(*C2);
        *C1  = *C1   - SUM*TAUIN;
        *C2  = *C2   - SUM*T2;
        /*   new nnz at TEMP and update C3 */
        SUM  =        VIN * (*C3);
        TEMP =      - SUM * TAUIN;
        *C3  = *C3  - SUM * T2;
        /*  generate Householder to annihilate the nonzero created at TEMP */
        *V    = TEMP;
        LAPACKE_slarfg_work( 2, C1, V, 1, TAU);
        VIN   = (*V);
        TAUIN = (*TAU);
        /*  Right 1 ==> C2 C3 */
        /* VIN     = VIN */
        T2  = TAUIN * (VIN);
        SUM = *C2   + VIN*(*C3);
        *C2 = *C2   - SUM*TAUIN;
        *C3 = *C3   - SUM*T2;
    }else if(uplo==PlasmaUpper){ 
        /*  
         * Do the corner for the upper case BIDIAG ==> Right then will
        *  create a new nnz. eliminate it and modify V TAU and then
        *  Left
        *             C(N-1, N-1)  C(N-1,N)        C1    C2 
        *             C(N  , N-1)  C(N  ,N)        TEMP  C3 
        *  For Left : use (TAU) and V. 
        *  For Right: use (TAU) and (V) as input. 
        */
        VIN   = (*V);
        TAUIN = (*TAU);
        /*  Right 1 ==> C1 C2 */
        /* VIN     = VIN */
        T2   = TAUIN*(VIN);
        SUM  = *C1  + VIN*(*C2);
        *C1  = *C1  - SUM*TAUIN;
        *C2  = *C2  - SUM*T2;
        /*   new nnz at TEMP and update C3 */
        SUM  =        VIN * (*C3);
        TEMP =      - SUM * TAUIN;
        *C3  = *C3  - SUM * T2;
        /*  generate Householder to annihilate the nonzero created at TEMP */
        *V    = TEMP;
        LAPACKE_slarfg_work( 2, C1, V, 1, TAU);
        VIN   = *V;
        TAUIN = (*TAU);
        /*  apply from the Left using the NEW V TAU to the remaining 2 elements [C2 C3] */
        /*  Left 2 ==> C2 */
        /*             C3 */
        VIN = (VIN);
        T2  = TAUIN*(VIN);
        SUM = *C2 + VIN*(*C3);
        *C2 = *C2 - SUM*TAUIN;
        *C3 = *C3 - SUM*T2;
    }
    return PLASMA_SUCCESS;
}