/* -- 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 dsyr2_(char *uplo, integer *n, doublereal *alpha,
doublereal *x, integer *incx, doublereal *y, integer *incy,
doublereal *a, integer *lda)
{
/* 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
=======
DSYR2 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.
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.
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.
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.
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 - 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. 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.
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 (*incx == 0) {
info = 5;
} else if (*incy == 0) {
info = 7;
} else if (*lda < max(1,*n)) {
info = 9;
}
if (info != 0) {
xerbla_("DSYR2 ", &info);
return 0;
}
/* Quick return if possible. */
if (*n == 0 || *alpha == 0.) {
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 <= *n; ++j) {
if (X(j) != 0. || Y(j) != 0.) {
temp1 = *alpha * Y(j);
temp2 = *alpha * X(j);
i__2 = j;
for (i = 1; i <= j; ++i) {
A(i,j) = A(i,j) + X(i) * temp1
+ Y(i) * temp2;
/* L10: */
}
}
/* L20: */
}
} else {
i__1 = *n;
for (j = 1; j <= *n; ++j) {
if (X(jx) != 0. || Y(jy) != 0.) {
temp1 = *alpha * Y(jy);
temp2 = *alpha * X(jx);
ix = kx;
iy = ky;
i__2 = j;
for (i = 1; i <= j; ++i) {
A(i,j) = A(i,j) + 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 <= *n; ++j) {
if (X(j) != 0. || Y(j) != 0.) {
temp1 = *alpha * Y(j);
temp2 = *alpha * X(j);
i__2 = *n;
for (i = j; i <= *n; ++i) {
A(i,j) = A(i,j) + X(i) * temp1
+ Y(i) * temp2;
/* L50: */
}
}
/* L60: */
}
} else {
i__1 = *n;
for (j = 1; j <= *n; ++j) {
if (X(jx) != 0. || Y(jy) != 0.) {
temp1 = *alpha * Y(jy);
temp2 = *alpha * X(jx);
ix = jx;
iy = jy;
i__2 = *n;
for (i = j; i <= *n; ++i) {
A(i,j) = A(i,j) + X(ix) * temp1
+ Y(iy) * temp2;
ix += *incx;
iy += *incy;
/* L70: */
}
}
jx += *incx;
jy += *incy;
/* L80: */
}
}
}
return 0;
/* End of DSYR2 . */
} /* dsyr2_ */