dsymv.c

SuperLU is a general purpose library for the direct solution of large, sparse, nonsymmetric systems

/*  -- translated by f2c (version 19940927).
   You must link the resulting object file with the libraries:
	-lf2c -lm   (in that order)
*/

#include "f2c.h"

/* Subroutine */ int dsymv_(char *uplo, integer *n, doublereal *alpha, 
	doublereal *a, integer *lda, doublereal *x, integer *incx, doublereal 
	*beta, doublereal *y, integer *incy)
{


    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2;

    /* Local variables */
    static integer info;
    static doublereal temp1, temp2;
    static integer i, j;
    extern logical lsame_(char *, char *);
    static integer ix, iy, jx, jy, kx, ky;
    extern /* Subroutine */ int xerbla_(char *, integer *);


/*  Purpose   
    =======   

    DSYMV  performs the matrix-vector  operation   

       y := alpha*A*x + beta*y,   

    where alpha and beta are scalars, x and y are n element vectors and   
    A is an n by n symmetric matrix.   

    Parameters   
    ==========   

    UPLO   - CHARACTER*1.   
             On entry, UPLO specifies whether the upper or lower   
             triangular part of the array A is to be referenced as   
             follows:   

                UPLO = 'U' or 'u'   Only the upper triangular part of A   
                                    is to be referenced.   

                UPLO = 'L' or 'l'   Only the lower triangular part of A   
                                    is to be referenced.   

             Unchanged on exit.   

    N      - INTEGER.   
             On entry, N specifies the order of the matrix A.   
             N must be at least zero.   
             Unchanged on exit.   

    ALPHA  - DOUBLE PRECISION.   
             On entry, ALPHA specifies the scalar alpha.   
             Unchanged on exit.   

    A      - DOUBLE PRECISION array of DIMENSION ( LDA, n ).   
             Before entry with  UPLO = 'U' or 'u', the leading n by n   
             upper triangular part of the array A must contain the upper 
  
             triangular part of the symmetric matrix and the strictly   
             lower triangular part of A is not referenced.   
             Before entry with UPLO = 'L' or 'l', the leading n by n   
             lower triangular part of the array A must contain the lower 
  
             triangular part of the symmetric matrix and the strictly   
             upper triangular part of A is not referenced.   
             Unchanged on exit.   

    LDA    - INTEGER.   
             On entry, LDA specifies the first dimension of A as declared 
  
             in the calling (sub) program. LDA must be at least   
             max( 1, n ).   
             Unchanged on exit.   

    X      - DOUBLE PRECISION array of dimension at least   
             ( 1 + ( n - 1 )*abs( INCX ) ).   
             Before entry, the incremented array X must contain the n   
             element vector x.   
             Unchanged on exit.   

    INCX   - INTEGER.   
             On entry, INCX specifies the increment for the elements of   
             X. INCX must not be zero.   
             Unchanged on exit.   

    BETA   - DOUBLE PRECISION.   
             On entry, BETA specifies the scalar beta. When BETA is   
             supplied as zero then Y need not be set on input.   
             Unchanged on exit.   

    Y      - DOUBLE PRECISION array of dimension at least   
             ( 1 + ( n - 1 )*abs( INCY ) ).   
             Before entry, the incremented array Y must contain the n   
             element vector y. On exit, Y is overwritten by the updated   
             vector y.   

    INCY   - INTEGER.   
             On entry, INCY specifies the increment for the elements of   
             Y. INCY must not be zero.   
             Unchanged on exit.   


    Level 2 Blas routine.   

    -- Written on 22-October-1986.   
       Jack Dongarra, Argonne National Lab.   
       Jeremy Du Croz, Nag Central Office.   
       Sven Hammarling, Nag Central Office.   
       Richard Hanson, Sandia National Labs.   



       Test the input parameters.   

    
   Parameter adjustments   
       Function Body */
#define X(I) x[(I)-1]
#define Y(I) y[(I)-1]

#define A(I,J) a[(I)-1 + ((J)-1)* ( *lda)]

    info = 0;
    if (! lsame_(uplo, "U") && ! lsame_(uplo, "L")) {
	info = 1;
    } else if (*n < 0) {
	info = 2;
    } else if (*lda < max(1,*n)) {
	info = 5;
    } else if (*incx == 0) {
	info = 7;
    } else if (*incy == 0) {
	info = 10;
    }
    if (info != 0) {
	xerbla_("DSYMV ", &info);
	return 0;
    }

/*     Quick return if possible. */

    if (*n == 0 || *alpha == 0. && *beta == 1.) {
	return 0;
    }

/*     Set up the start points in  X  and  Y. */

    if (*incx > 0) {
	kx = 1;
    } else {
	kx = 1 - (*n - 1) * *incx;
    }
    if (*incy > 0) {
	ky = 1;
    } else {
	ky = 1 - (*n - 1) * *incy;
    }

/*     Start the operations. In this version the elements of A are   
       accessed sequentially with one pass through the triangular part   
       of A.   

       First form  y := beta*y. */

    if (*beta != 1.) {
	if (*incy == 1) {
	    if (*beta == 0.) {
		i__1 = *n;
		for (i = 1; i <= *n; ++i) {
		    Y(i) = 0.;
/* L10: */
		}
	    } else {
		i__1 = *n;
		for (i = 1; i <= *n; ++i) {
		    Y(i) = *beta * Y(i);
/* L20: */
		}
	    }
	} else {
	    iy = ky;
	    if (*beta == 0.) {
		i__1 = *n;
		for (i = 1; i <= *n; ++i) {
		    Y(iy) = 0.;
		    iy += *incy;
/* L30: */
		}
	    } else {
		i__1 = *n;
		for (i = 1; i <= *n; ++i) {
		    Y(iy) = *beta * Y(iy);
		    iy += *incy;
/* L40: */
		}
	    }
	}
    }
    if (*alpha == 0.) {
	return 0;
    }
    if (lsame_(uplo, "U")) {

/*        Form  y  when A is stored in upper triangle. */

	if (*incx == 1 && *incy == 1) {
	    i__1 = *n;
	    for (j = 1; j <= *n; ++j) {
		temp1 = *alpha * X(j);
		temp2 = 0.;
		i__2 = j - 1;
		for (i = 1; i <= j-1; ++i) {
		    Y(i) += temp1 * A(i,j);
		    temp2 += A(i,j) * X(i);
/* L50: */
		}
		Y(j) = Y(j) + temp1 * A(j,j) + *alpha * temp2;
/* L60: */
	    }
	} else {
	    jx = kx;
	    jy = ky;
	    i__1 = *n;
	    for (j = 1; j <= *n; ++j) {
		temp1 = *alpha * X(jx);
		temp2 = 0.;
		ix = kx;
		iy = ky;
		i__2 = j - 1;
		for (i = 1; i <= j-1; ++i) {
		    Y(iy) += temp1 * A(i,j);
		    temp2 += A(i,j) * X(ix);
		    ix += *incx;
		    iy += *incy;
/* L70: */
		}
		Y(jy) = Y(jy) + temp1 * A(j,j) + *alpha * temp2;
		jx += *incx;
		jy += *incy;
/* L80: */
	    }
	}
    } else {

/*        Form  y  when A is stored in lower triangle. */

	if (*incx == 1 && *incy == 1) {
	    i__1 = *n;
	    for (j = 1; j <= *n; ++j) {
		temp1 = *alpha * X(j);
		temp2 = 0.;
		Y(j) += temp1 * A(j,j);
		i__2 = *n;
		for (i = j + 1; i <= *n; ++i) {
		    Y(i) += temp1 * A(i,j);
		    temp2 += A(i,j) * X(i);
/* L90: */
		}
		Y(j) += *alpha * temp2;
/* L100: */
	    }
	} else {
	    jx = kx;
	    jy = ky;
	    i__1 = *n;
	    for (j = 1; j <= *n; ++j) {
		temp1 = *alpha * X(jx);
		temp2 = 0.;
		Y(jy) += temp1 * A(j,j);
		ix = jx;
		iy = jy;
		i__2 = *n;
		for (i = j + 1; i <= *n; ++i) {
		    ix += *incx;
		    iy += *incy;
		    Y(iy) += temp1 * A(i,j);
		    temp2 += A(i,j) * X(ix);
/* L110: */
		}
		Y(jy) += *alpha * temp2;
		jx += *incx;
		jy += *incy;
/* L120: */
	    }
	}
    }

    return 0;

/*     End of DSYMV . */

} /* dsymv_ */