/* -- translated by f2c (version 20100827).
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*/
#include "f2c.h"
/* Table of constant values */
static integer c__1 = 1;
static doublereal c_b10 = -1.;
static doublereal c_b12 = 1.;
/* > \brief \b DPOTF2 computes the Cholesky factorization of a symmetric/Hermitian positive definite matrix (u
nblocked algorithm).
=========== DOCUMENTATION ===========
Online html documentation available at
http://www.netlib.org/lapack/explore-html/
> \htmlonly
> Download DPOTF2 + dependencies
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f">
> [TXT]</a>
> \endhtmlonly
Definition:
===========
SUBROUTINE DPOTF2( UPLO, N, A, LDA, INFO )
CHARACTER UPLO
INTEGER INFO, LDA, N
DOUBLE PRECISION A( LDA, * )
> \par Purpose:
=============
>
> \verbatim
>
> DPOTF2 computes the Cholesky factorization of a real symmetric
> positive definite matrix A.
>
> The factorization has the form
> A = U**T * U , if UPLO = 'U', or
> A = L * L**T, 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.
> \endverbatim
Arguments:
==========
> \param[in] UPLO
> \verbatim
> UPLO is CHARACTER*1
> Specifies whether the upper or lower triangular part of the
> symmetric matrix A is stored.
> = 'U': Upper triangular
> = 'L': Lower triangular
> \endverbatim
>
> \param[in] N
> \verbatim
> N is INTEGER
> The order of the matrix A. N >= 0.
> \endverbatim
>
> \param[in,out] A
> \verbatim
> A is 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**T *U or A = L*L**T.
> \endverbatim
>
> \param[in] LDA
> \verbatim
> LDA is INTEGER
> The leading dimension of the array A. LDA >= max(1,N).
> \endverbatim
>
> \param[out] INFO
> \verbatim
> INFO is 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.
> \endverbatim
Authors:
========
> \author Univ. of Tennessee
> \author Univ. of California Berkeley
> \author Univ. of Colorado Denver
> \author NAG Ltd.
> \date September 2012
> \ingroup doublePOcomputational
=====================================================================
Subroutine */ int igraphdpotf2_(char *uplo, integer *n, doublereal *a, integer *
lda, integer *info)
{
/* System generated locals */
integer a_dim1, a_offset, i__1, i__2, i__3;
doublereal d__1;
/* Builtin functions */
double sqrt(doublereal);
/* Local variables */
integer j;
doublereal ajj;
extern doublereal igraphddot_(integer *, doublereal *, integer *, doublereal *,
integer *);
extern /* Subroutine */ int igraphdscal_(integer *, doublereal *, doublereal *,
integer *);
extern logical igraphlsame_(char *, char *);
extern /* Subroutine */ int igraphdgemv_(char *, integer *, integer *,
doublereal *, doublereal *, integer *, doublereal *, integer *,
doublereal *, doublereal *, integer *);
logical upper;
extern logical igraphdisnan_(doublereal *);
extern /* Subroutine */ int igraphxerbla_(char *, integer *, ftnlen);
/* -- LAPACK computational routine (version 3.4.2) --
-- LAPACK is a software package provided by Univ. of Tennessee, --
-- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
September 2012
=====================================================================
Test the input parameters.
Parameter adjustments */
a_dim1 = *lda;
a_offset = 1 + a_dim1;
a -= a_offset;
/* Function Body */
*info = 0;
upper = igraphlsame_(uplo, "U");
if (! upper && ! igraphlsame_(uplo, "L")) {
*info = -1;
} else if (*n < 0) {
*info = -2;
} else if (*lda < max(1,*n)) {
*info = -4;
}
if (*info != 0) {
i__1 = -(*info);
igraphxerbla_("DPOTF2", &i__1, (ftnlen)6);
return 0;
}
/* Quick return if possible */
if (*n == 0) {
return 0;
}
if (upper) {
/* Compute the Cholesky factorization A = U**T *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[j + j * a_dim1] - igraphddot_(&i__2, &a[j * a_dim1 + 1], &c__1,
&a[j * a_dim1 + 1], &c__1);
if (ajj <= 0. || igraphdisnan_(&ajj)) {
a[j + j * a_dim1] = ajj;
goto L30;
}
ajj = sqrt(ajj);
a[j + j * a_dim1] = ajj;
/* Compute elements J+1:N of row J. */
if (j < *n) {
i__2 = j - 1;
i__3 = *n - j;
igraphdgemv_("Transpose", &i__2, &i__3, &c_b10, &a[(j + 1) * a_dim1
+ 1], lda, &a[j * a_dim1 + 1], &c__1, &c_b12, &a[j + (
j + 1) * a_dim1], lda);
i__2 = *n - j;
d__1 = 1. / ajj;
igraphdscal_(&i__2, &d__1, &a[j + (j + 1) * a_dim1], lda);
}
/* L10: */
}
} else {
/* Compute the Cholesky factorization A = L*L**T. */
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[j + j * a_dim1] - igraphddot_(&i__2, &a[j + a_dim1], lda, &a[j
+ a_dim1], lda);
if (ajj <= 0. || igraphdisnan_(&ajj)) {
a[j + j * a_dim1] = ajj;
goto L30;
}
ajj = sqrt(ajj);
a[j + j * a_dim1] = ajj;
/* Compute elements J+1:N of column J. */
if (j < *n) {
i__2 = *n - j;
i__3 = j - 1;
igraphdgemv_("No transpose", &i__2, &i__3, &c_b10, &a[j + 1 +
a_dim1], lda, &a[j + a_dim1], lda, &c_b12, &a[j + 1 +
j * a_dim1], &c__1);
i__2 = *n - j;
d__1 = 1. / ajj;
igraphdscal_(&i__2, &d__1, &a[j + 1 + j * a_dim1], &c__1);
}
/* L20: */
}
}
goto L40;
L30:
*info = j;
L40:
return 0;
/* End of DPOTF2 */
} /* igraphdpotf2_ */