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/* spttrs.f -- translated by f2c (version 20061008).
You must link the resulting object file with libf2c:
on Microsoft Windows system, link with libf2c.lib;
on Linux or Unix systems, link with .../path/to/libf2c.a -lm
or, if you install libf2c.a in a standard place, with -lf2c -lm
-- in that order, at the end of the command line, as in
cc *.o -lf2c -lm
Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,
http://www.netlib.org/f2c/libf2c.zip
*/
#include "f2c.h"
#include "blaswrap.h"
/* Table of constant values */
static integer c__1 = 1;
static integer c_n1 = -1;
/* Subroutine */ int spttrs_(integer *n, integer *nrhs, real *d__, real *e,
real *b, integer *ldb, integer *info)
{
/* System generated locals */
integer b_dim1, b_offset, i__1, i__2, i__3;
/* Local variables */
integer j, jb, nb;
extern /* Subroutine */ int sptts2_(integer *, integer *, real *, real *,
real *, integer *), xerbla_(char *, integer *);
extern integer ilaenv_(integer *, char *, char *, integer *, integer *,
integer *, integer *);
/* -- LAPACK routine (version 3.2) -- */
/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/* November 2006 */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* Purpose */
/* ======= */
/* SPTTRS solves a tridiagonal system of the form */
/* A * X = B */
/* using the L*D*L' factorization of A computed by SPTTRF. D is a */
/* diagonal matrix specified in the vector D, L is a unit bidiagonal */
/* matrix whose subdiagonal is specified in the vector E, and X and B */
/* are N by NRHS matrices. */
/* Arguments */
/* ========= */
/* N (input) INTEGER */
/* The order of the tridiagonal matrix A. N >= 0. */
/* NRHS (input) INTEGER */
/* The number of right hand sides, i.e., the number of columns */
/* of the matrix B. NRHS >= 0. */
/* D (input) REAL array, dimension (N) */
/* The n diagonal elements of the diagonal matrix D from the */
/* L*D*L' factorization of A. */
/* E (input) REAL array, dimension (N-1) */
/* The (n-1) subdiagonal elements of the unit bidiagonal factor */
/* L from the L*D*L' factorization of A. E can also be regarded */
/* as the superdiagonal of the unit bidiagonal factor U from the */
/* factorization A = U'*D*U. */
/* B (input/output) REAL array, dimension (LDB,NRHS) */
/* On entry, the right hand side vectors B for the system of */
/* linear equations. */
/* On exit, the solution vectors, X. */
/* LDB (input) INTEGER */
/* The leading dimension of the array B. LDB >= max(1,N). */
/* INFO (output) INTEGER */
/* = 0: successful exit */
/* < 0: if INFO = -k, the k-th argument had an illegal value */
/* ===================================================================== */
/* .. Local Scalars .. */
/* .. */
/* .. External Functions .. */
/* .. */
/* .. External Subroutines .. */
/* .. */
/* .. Intrinsic Functions .. */
/* .. */
/* .. Executable Statements .. */
/* Test the input arguments. */
/* Parameter adjustments */
--d__;
--e;
b_dim1 = *ldb;
b_offset = 1 + b_dim1;
b -= b_offset;
/* Function Body */
*info = 0;
if (*n < 0) {
*info = -1;
} else if (*nrhs < 0) {
*info = -2;
} else if (*ldb < max(1,*n)) {
*info = -6;
}
if (*info != 0) {
i__1 = -(*info);
xerbla_("SPTTRS", &i__1);
return 0;
}
/* Quick return if possible */
if (*n == 0 || *nrhs == 0) {
return 0;
}
/* Determine the number of right-hand sides to solve at a time. */
if (*nrhs == 1) {
nb = 1;
} else {
/* Computing MAX */
i__1 = 1, i__2 = ilaenv_(&c__1, "SPTTRS", " ", n, nrhs, &c_n1, &c_n1);
nb = max(i__1,i__2);
}
if (nb >= *nrhs) {
sptts2_(n, nrhs, &d__[1], &e[1], &b[b_offset], ldb);
} else {
i__1 = *nrhs;
i__2 = nb;
for (j = 1; i__2 < 0 ? j >= i__1 : j <= i__1; j += i__2) {
/* Computing MIN */
i__3 = *nrhs - j + 1;
jb = min(i__3,nb);
sptts2_(n, &jb, &d__[1], &e[1], &b[j * b_dim1 + 1], ldb);
/* L10: */
}
}
return 0;
/* End of SPTTRS */
} /* spttrs_ */
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