#include "clapack.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 */ integer i__, j, ix, iy, jx, jy, kx, ky, info; doublereal temp1, temp2; extern logical lsame_(char *, char *); extern /* Subroutine */ int xerbla_(char *, integer *); /* .. Scalar Arguments .. */ /* .. */ /* .. Array Arguments .. */ /* .. */ /* 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. */ /* 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 - 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. */ /* .. 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_("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 <= i__1; ++j) { if (x[j] != 0. || y[j] != 0.) { 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. || y[jy] != 0.) { 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. || y[j] != 0.) { 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. || y[jy] != 0.) { 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 DSYR2 . */ } /* dsyr2_ */