ssyr2.c

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/* ssyr2.f -- translated by f2c (version 20061008).
   You must link the resulting object file with libf2c:
        on Microsoft Windows system, link with libf2c.lib;
        on Linux or Unix systems, link with .../path/to/libf2c.a -lm
        or, if you install libf2c.a in a standard place, with -lf2c -lm
        -- in that order, at the end of the command line, as in
                cc *.o -lf2c -lm
        Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,

                http://www.netlib.org/f2c/libf2c.zip
*/

#include "f2c.h"
#include "blaswrap.h"

/* Subroutine */ int ssyr2_(char *uplo, integer *n, real *alpha, real *x, 
        integer *incx, real *y, integer *incy, real *a, integer *lda)
{
    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2;

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

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */

/*  Purpose */
/*  ======= */

/*  SSYR2  performs the symmetric rank 2 operation */

/*     A := alpha*x*y' + alpha*y*x' + A, */

/*  where alpha is a scalar, x and y are n element vectors and A is an n */
/*  by n symmetric matrix. */

/*  Arguments */
/*  ========== */

/*  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  - REAL            . */
/*           On entry, ALPHA specifies the scalar alpha. */
/*           Unchanged on exit. */

/*  X      - REAL             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. */

/*  Y      - REAL             array of dimension at least */
/*           ( 1 + ( n - 1 )*abs( INCY ) ). */
/*           Before entry, the incremented array Y must contain the n */
/*           element vector y. */
/*           Unchanged on exit. */

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

/*  A      - REAL             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. On exit, the */
/*           upper triangular part of the array A is overwritten by the */
/*           upper triangular part of the updated matrix. */
/*           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. On exit, the */
/*           lower triangular part of the array A is overwritten by the */
/*           lower triangular part of the updated matrix. */

/*  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. */


/*  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. */


/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. External Functions .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */
/*     .. Intrinsic Functions .. */
/*     .. */

/*     Test the input parameters. */

    /* Parameter adjustments */
    --x;
    --y;
    a_dim1 = *lda;
    a_offset = 1 + a_dim1;
    a -= a_offset;

    /* Function Body */
    info = 0;
    if (! lsame_(uplo, "U") && ! lsame_(uplo, "L")) {
        info = 1;
    } else if (*n < 0) {
        info = 2;
    } else if (*incx == 0) {
        info = 5;
    } else if (*incy == 0) {
        info = 7;
    } else if (*lda < max(1,*n)) {
        info = 9;
    }
    if (info != 0) {
        xerbla_("SSYR2 ", &info);
        return 0;
    }

/*     Quick return if possible. */

    if (*n == 0 || *alpha == 0.f) {
        return 0;
    }

/*     Set up the start points in X and Y if the increments are not both */
/*     unity. */

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

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

    if (lsame_(uplo, "U")) {

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

        if (*incx == 1 && *incy == 1) {
            i__1 = *n;
            for (j = 1; j <= i__1; ++j) {
                if (x[j] != 0.f || y[j] != 0.f) {
                    temp1 = *alpha * y[j];
                    temp2 = *alpha * x[j];
                    i__2 = j;
                    for (i__ = 1; i__ <= i__2; ++i__) {
                        a[i__ + j * a_dim1] = a[i__ + j * a_dim1] + x[i__] * 
                                temp1 + y[i__] * temp2;
/* L10: */
                    }
                }
/* L20: */
            }
        } else {
            i__1 = *n;
            for (j = 1; j <= i__1; ++j) {
                if (x[jx] != 0.f || y[jy] != 0.f) {
                    temp1 = *alpha * y[jy];
                    temp2 = *alpha * x[jx];
                    ix = kx;
                    iy = ky;
                    i__2 = j;
                    for (i__ = 1; i__ <= i__2; ++i__) {
                        a[i__ + j * a_dim1] = a[i__ + j * a_dim1] + x[ix] * 
                                temp1 + y[iy] * temp2;
                        ix += *incx;
                        iy += *incy;
/* L30: */
                    }
                }
                jx += *incx;
                jy += *incy;
/* L40: */
            }
        }
    } else {

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

        if (*incx == 1 && *incy == 1) {
            i__1 = *n;
            for (j = 1; j <= i__1; ++j) {
                if (x[j] != 0.f || y[j] != 0.f) {
                    temp1 = *alpha * y[j];
                    temp2 = *alpha * x[j];
                    i__2 = *n;
                    for (i__ = j; i__ <= i__2; ++i__) {
                        a[i__ + j * a_dim1] = a[i__ + j * a_dim1] + x[i__] * 
                                temp1 + y[i__] * temp2;
/* L50: */
                    }
                }
/* L60: */
            }
        } else {
            i__1 = *n;
            for (j = 1; j <= i__1; ++j) {
                if (x[jx] != 0.f || y[jy] != 0.f) {
                    temp1 = *alpha * y[jy];
                    temp2 = *alpha * x[jx];
                    ix = jx;
                    iy = jy;
                    i__2 = *n;
                    for (i__ = j; i__ <= i__2; ++i__) {
                        a[i__ + j * a_dim1] = a[i__ + j * a_dim1] + x[ix] * 
                                temp1 + y[iy] * temp2;
                        ix += *incx;
                        iy += *incy;
/* L70: */
                    }
                }
                jx += *incx;
                jy += *incy;
/* L80: */
            }
        }
    }

    return 0;

/*     End of SSYR2 . */

} /* ssyr2_ */