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/* dptts2.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"
/* Subroutine */ int dptts2_(integer *n, integer *nrhs, doublereal *d__,
doublereal *e, doublereal *b, integer *ldb)
{
/* System generated locals */
integer b_dim1, b_offset, i__1, i__2;
doublereal d__1;
/* Local variables */
integer i__, j;
extern /* Subroutine */ int dscal_(integer *, doublereal *, doublereal *,
integer *);
/* -- LAPACK routine (version 3.2) -- */
/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/* November 2006 */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* Purpose */
/* ======= */
/* DPTTS2 solves a tridiagonal system of the form */
/* A * X = B */
/* using the L*D*L' factorization of A computed by DPTTRF. 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) DOUBLE PRECISION array, dimension (N) */
/* The n diagonal elements of the diagonal matrix D from the */
/* L*D*L' factorization of A. */
/* E (input) DOUBLE PRECISION 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) DOUBLE PRECISION 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). */
/* ===================================================================== */
/* .. Local Scalars .. */
/* .. */
/* .. External Subroutines .. */
/* .. */
/* .. Executable Statements .. */
/* Quick return if possible */
/* Parameter adjustments */
--d__;
--e;
b_dim1 = *ldb;
b_offset = 1 + b_dim1;
b -= b_offset;
/* Function Body */
if (*n <= 1) {
if (*n == 1) {
d__1 = 1. / d__[1];
dscal_(nrhs, &d__1, &b[b_offset], ldb);
}
return 0;
}
/* Solve A * X = B using the factorization A = L*D*L', */
/* overwriting each right hand side vector with its solution. */
i__1 = *nrhs;
for (j = 1; j <= i__1; ++j) {
/* Solve L * x = b. */
i__2 = *n;
for (i__ = 2; i__ <= i__2; ++i__) {
b[i__ + j * b_dim1] -= b[i__ - 1 + j * b_dim1] * e[i__ - 1];
/* L10: */
}
/* Solve D * L' * x = b. */
b[*n + j * b_dim1] /= d__[*n];
for (i__ = *n - 1; i__ >= 1; --i__) {
b[i__ + j * b_dim1] = b[i__ + j * b_dim1] / d__[i__] - b[i__ + 1
+ j * b_dim1] * e[i__];
/* L20: */
}
/* L30: */
}
return 0;
/* End of DPTTS2 */
} /* dptts2_ */
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