hypre/lapack/dpotf2.c

#include "../blas/hypre_blas.h"
#include "hypre_lapack.h"
#include "f2c.h"

/* Subroutine */ HYPRE_Int dpotf2_(char *uplo, integer *n, doublereal *a, integer *
	lda, integer *info)
{
/*  -- LAPACK routine (version 3.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       February 29, 1992   


    Purpose   
    =======   

    DPOTF2 computes the Cholesky factorization of a real symmetric   
    positive definite matrix A.   

    The factorization has the form   
       A = U' * U ,  if UPLO = 'U', or   
       A = L  * L',  if UPLO = 'L',   
    where U is an upper triangular matrix and L is lower triangular.   

    This is the unblocked version of the algorithm, calling Level 2 BLAS.   

    Arguments   
    =========   

    UPLO    (input) CHARACTER*1   
            Specifies whether the upper or lower triangular part of the   
            symmetric matrix A is stored.   
            = 'U':  Upper triangular   
            = 'L':  Lower triangular   

    N       (input) INTEGER   
            The order of the matrix A.  N >= 0.   

    A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)   
            On entry, the symmetric matrix A.  If UPLO = 'U', the leading   
            n by n upper triangular part of A contains the upper   
            triangular part of the matrix A, and the strictly lower   
            triangular part of A is not referenced.  If UPLO = 'L', the   
            leading n by n lower triangular part of A contains the lower   
            triangular part of the matrix A, and the strictly upper   
            triangular part of A is not referenced.   

            On exit, if INFO = 0, the factor U or L from the Cholesky   
            factorization A = U'*U  or A = L*L'.   

    LDA     (input) INTEGER   
            The leading dimension of the array A.  LDA >= max(1,N).   

    INFO    (output) INTEGER   
            = 0: successful exit   
            < 0: if INFO = -k, the k-th argument had an illegal value   
            > 0: if INFO = k, the leading minor of order k is not   
                 positive definite, and the factorization could not be   
                 completed.   

    =====================================================================   


       Test the input parameters.   

       Parameter adjustments */
    /* Table of constant values */
    static integer c__1 = 1;
    static doublereal c_b10 = -1.;
    static doublereal c_b12 = 1.;
    
    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2, i__3;
    doublereal d__1;
    /* Builtin functions */
    double sqrt(doublereal);
    /* Local variables */
    extern doublereal ddot_(integer *, doublereal *, integer *, doublereal *, 
	    integer *);
    static integer j;
    extern /* Subroutine */ HYPRE_Int dscal_(integer *, doublereal *, doublereal *, 
	    integer *);
    extern logical lsame_(char *, char *);
    extern /* Subroutine */ HYPRE_Int dgemv_(char *, integer *, integer *, 
	    doublereal *, doublereal *, integer *, doublereal *, integer *, 
	    doublereal *, doublereal *, integer *);
    static logical upper;
    extern /* Subroutine */ HYPRE_Int xerbla_(char *, integer *);
    static doublereal ajj;
#define a_ref(a_1,a_2) a[(a_2)*a_dim1 + a_1]


    a_dim1 = *lda;
    a_offset = 1 + a_dim1 * 1;
    a -= a_offset;

    /* Function Body */
    *info = 0;
    upper = lsame_(uplo, "U");
    if (! upper && ! lsame_(uplo, "L")) {
	*info = -1;
    } else if (*n < 0) {
	*info = -2;
    } else if (*lda < max(1,*n)) {
	*info = -4;
    }
    if (*info != 0) {
	i__1 = -(*info);
	xerbla_("DPOTF2", &i__1);
	return 0;
    }

/*     Quick return if possible */

    if (*n == 0) {
	return 0;
    }

    if (upper) {

/*        Compute the Cholesky factorization A = U'*U. */

	i__1 = *n;
	for (j = 1; j <= i__1; ++j) {

/*           Compute U(J,J) and test for non-positive-definiteness. */

	    i__2 = j - 1;
	    ajj = a_ref(j, j) - ddot_(&i__2, &a_ref(1, j), &c__1, &a_ref(1, j)
		    , &c__1);
	    if (ajj <= 0.) {
		a_ref(j, j) = ajj;
		goto L30;
	    }
	    ajj = sqrt(ajj);
	    a_ref(j, j) = ajj;

/*           Compute elements J+1:N of row J. */

	    if (j < *n) {
		i__2 = j - 1;
		i__3 = *n - j;
		dgemv_("Transpose", &i__2, &i__3, &c_b10, &a_ref(1, j + 1), 
			lda, &a_ref(1, j), &c__1, &c_b12, &a_ref(j, j + 1), 
			lda);
		i__2 = *n - j;
		d__1 = 1. / ajj;
		dscal_(&i__2, &d__1, &a_ref(j, j + 1), lda);
	    }
/* L10: */
	}
    } else {

/*        Compute the Cholesky factorization A = L*L'. */

	i__1 = *n;
	for (j = 1; j <= i__1; ++j) {

/*           Compute L(J,J) and test for non-positive-definiteness. */

	    i__2 = j - 1;
	    ajj = a_ref(j, j) - ddot_(&i__2, &a_ref(j, 1), lda, &a_ref(j, 1), 
		    lda);
	    if (ajj <= 0.) {
		a_ref(j, j) = ajj;
		goto L30;
	    }
	    ajj = sqrt(ajj);
	    a_ref(j, j) = ajj;

/*           Compute elements J+1:N of column J. */

	    if (j < *n) {
		i__2 = *n - j;
		i__3 = j - 1;
		dgemv_("No transpose", &i__2, &i__3, &c_b10, &a_ref(j + 1, 1),
			 lda, &a_ref(j, 1), lda, &c_b12, &a_ref(j + 1, j), &
			c__1);
		i__2 = *n - j;
		d__1 = 1. / ajj;
		dscal_(&i__2, &d__1, &a_ref(j + 1, j), &c__1);
	    }
/* L20: */
	}
    }
    goto L40;

L30:
    *info = j;

L40:
    return 0;

/*     End of DPOTF2 */

} /* dpotf2_ */

#undef a_ref