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/* spbtrs.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;
/* Subroutine */ int spbtrs_(char *uplo, integer *n, integer *kd, integer *
nrhs, real *ab, integer *ldab, real *b, integer *ldb, integer *info)
{
/* System generated locals */
integer ab_dim1, ab_offset, b_dim1, b_offset, i__1;
/* Local variables */
integer j;
extern logical lsame_(char *, char *);
logical upper;
extern /* Subroutine */ int stbsv_(char *, char *, char *, integer *,
integer *, real *, integer *, real *, integer *), xerbla_(char *, integer *);
/* -- LAPACK routine (version 3.2) -- */
/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/* November 2006 */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* Purpose */
/* ======= */
/* SPBTRS solves a system of linear equations A*X = B with a symmetric */
/* positive definite band matrix A using the Cholesky factorization */
/* A = U**T*U or A = L*L**T computed by SPBTRF. */
/* Arguments */
/* ========= */
/* UPLO (input) CHARACTER*1 */
/* = 'U': Upper triangular factor stored in AB; */
/* = 'L': Lower triangular factor stored in AB. */
/* N (input) INTEGER */
/* The order of the matrix A. N >= 0. */
/* KD (input) INTEGER */
/* The number of superdiagonals of the matrix A if UPLO = 'U', */
/* or the number of subdiagonals if UPLO = 'L'. KD >= 0. */
/* NRHS (input) INTEGER */
/* The number of right hand sides, i.e., the number of columns */
/* of the matrix B. NRHS >= 0. */
/* AB (input) REAL array, dimension (LDAB,N) */
/* The triangular factor U or L from the Cholesky factorization */
/* A = U**T*U or A = L*L**T of the band matrix A, stored in the */
/* first KD+1 rows of the array. The j-th column of U or L is */
/* stored in the j-th column of the array AB as follows: */
/* if UPLO ='U', AB(kd+1+i-j,j) = U(i,j) for max(1,j-kd)<=i<=j; */
/* if UPLO ='L', AB(1+i-j,j) = L(i,j) for j<=i<=min(n,j+kd). */
/* LDAB (input) INTEGER */
/* The leading dimension of the array AB. LDAB >= KD+1. */
/* B (input/output) REAL array, dimension (LDB,NRHS) */
/* On entry, the right hand side matrix B. */
/* On exit, the solution matrix X. */
/* LDB (input) INTEGER */
/* The leading dimension of the array B. LDB >= max(1,N). */
/* INFO (output) INTEGER */
/* = 0: successful exit */
/* < 0: if INFO = -i, the i-th argument had an illegal value */
/* ===================================================================== */
/* .. Local Scalars .. */
/* .. */
/* .. External Functions .. */
/* .. */
/* .. External Subroutines .. */
/* .. */
/* .. Intrinsic Functions .. */
/* .. */
/* .. Executable Statements .. */
/* Test the input parameters. */
/* Parameter adjustments */
ab_dim1 = *ldab;
ab_offset = 1 + ab_dim1;
ab -= ab_offset;
b_dim1 = *ldb;
b_offset = 1 + b_dim1;
b -= b_offset;
/* Function Body */
*info = 0;
upper = lsame_(uplo, "U");
if (! upper && ! lsame_(uplo, "L")) {
*info = -1;
} else if (*n < 0) {
*info = -2;
} else if (*kd < 0) {
*info = -3;
} else if (*nrhs < 0) {
*info = -4;
} else if (*ldab < *kd + 1) {
*info = -6;
} else if (*ldb < max(1,*n)) {
*info = -8;
}
if (*info != 0) {
i__1 = -(*info);
xerbla_("SPBTRS", &i__1);
return 0;
}
/* Quick return if possible */
if (*n == 0 || *nrhs == 0) {
return 0;
}
if (upper) {
/* Solve A*X = B where A = U'*U. */
i__1 = *nrhs;
for (j = 1; j <= i__1; ++j) {
/* Solve U'*X = B, overwriting B with X. */
stbsv_("Upper", "Transpose", "Non-unit", n, kd, &ab[ab_offset],
ldab, &b[j * b_dim1 + 1], &c__1);
/* Solve U*X = B, overwriting B with X. */
stbsv_("Upper", "No transpose", "Non-unit", n, kd, &ab[ab_offset],
ldab, &b[j * b_dim1 + 1], &c__1);
/* L10: */
}
} else {
/* Solve A*X = B where A = L*L'. */
i__1 = *nrhs;
for (j = 1; j <= i__1; ++j) {
/* Solve L*X = B, overwriting B with X. */
stbsv_("Lower", "No transpose", "Non-unit", n, kd, &ab[ab_offset],
ldab, &b[j * b_dim1 + 1], &c__1);
/* Solve L'*X = B, overwriting B with X. */
stbsv_("Lower", "Transpose", "Non-unit", n, kd, &ab[ab_offset],
ldab, &b[j * b_dim1 + 1], &c__1);
/* L20: */
}
}
return 0;
/* End of SPBTRS */
} /* spbtrs_ */
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