#include "clapack.h"

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

/*  SSYMV  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. */

/*  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. */

/*  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. */
/*           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      - 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. */

/*  BETA   - REAL            . */
/*           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      - REAL             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. */


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

/*     Test the input parameters. */

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

    /* Function Body */
    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_("SSYMV ", &info);
	return 0;
    }

/*     Quick return if possible. */

    if (*n == 0 || *alpha == 0.f && *beta == 1.f) {
	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.f) {
	if (*incy == 1) {
	    if (*beta == 0.f) {
		i__1 = *n;
		for (i__ = 1; i__ <= i__1; ++i__) {
		    y[i__] = 0.f;
/* L10: */
		}
	    } else {
		i__1 = *n;
		for (i__ = 1; i__ <= i__1; ++i__) {
		    y[i__] = *beta * y[i__];
/* L20: */
		}
	    }
	} else {
	    iy = ky;
	    if (*beta == 0.f) {
		i__1 = *n;
		for (i__ = 1; i__ <= i__1; ++i__) {
		    y[iy] = 0.f;
		    iy += *incy;
/* L30: */
		}
	    } else {
		i__1 = *n;
		for (i__ = 1; i__ <= i__1; ++i__) {
		    y[iy] = *beta * y[iy];
		    iy += *incy;
/* L40: */
		}
	    }
	}
    }
    if (*alpha == 0.f) {
	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 <= i__1; ++j) {
		temp1 = *alpha * x[j];
		temp2 = 0.f;
		i__2 = j - 1;
		for (i__ = 1; i__ <= i__2; ++i__) {
		    y[i__] += temp1 * a[i__ + j * a_dim1];
		    temp2 += a[i__ + j * a_dim1] * x[i__];
/* L50: */
		}
		y[j] = y[j] + temp1 * a[j + j * a_dim1] + *alpha * temp2;
/* L60: */
	    }
	} else {
	    jx = kx;
	    jy = ky;
	    i__1 = *n;
	    for (j = 1; j <= i__1; ++j) {
		temp1 = *alpha * x[jx];
		temp2 = 0.f;
		ix = kx;
		iy = ky;
		i__2 = j - 1;
		for (i__ = 1; i__ <= i__2; ++i__) {
		    y[iy] += temp1 * a[i__ + j * a_dim1];
		    temp2 += a[i__ + j * a_dim1] * x[ix];
		    ix += *incx;
		    iy += *incy;
/* L70: */
		}
		y[jy] = y[jy] + temp1 * a[j + j * a_dim1] + *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 <= i__1; ++j) {
		temp1 = *alpha * x[j];
		temp2 = 0.f;
		y[j] += temp1 * a[j + j * a_dim1];
		i__2 = *n;
		for (i__ = j + 1; i__ <= i__2; ++i__) {
		    y[i__] += temp1 * a[i__ + j * a_dim1];
		    temp2 += a[i__ + j * a_dim1] * x[i__];
/* L90: */
		}
		y[j] += *alpha * temp2;
/* L100: */
	    }
	} else {
	    jx = kx;
	    jy = ky;
	    i__1 = *n;
	    for (j = 1; j <= i__1; ++j) {
		temp1 = *alpha * x[jx];
		temp2 = 0.f;
		y[jy] += temp1 * a[j + j * a_dim1];
		ix = jx;
		iy = jy;
		i__2 = *n;
		for (i__ = j + 1; i__ <= i__2; ++i__) {
		    ix += *incx;
		    iy += *incy;
		    y[iy] += temp1 * a[i__ + j * a_dim1];
		    temp2 += a[i__ + j * a_dim1] * x[ix];
/* L110: */
		}
		y[jy] += *alpha * temp2;
		jx += *incx;
		jy += *incy;
/* L120: */
	    }
	}
    }

    return 0;

/*     End of SSYMV . */

} /* ssymv_ */
