stbtrs.c

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/* stbtrs.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 stbtrs_(char *uplo, char *trans, char *diag, 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 *);
    logical nounit;


/*  -- LAPACK routine (version 3.2) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/*     November 2006 */

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */

/*  Purpose */
/*  ======= */

/*  STBTRS solves a triangular system of the form */

/*     A * X = B  or  A**T * X = B, */

/*  where A is a triangular band matrix of order N, and B is an */
/*  N-by NRHS matrix.  A check is made to verify that A is nonsingular. */

/*  Arguments */
/*  ========= */

/*  UPLO    (input) CHARACTER*1 */
/*          = 'U':  A is upper triangular; */
/*          = 'L':  A is lower triangular. */

/*  TRANS   (input) CHARACTER*1 */
/*          Specifies the form the system of equations: */
/*          = 'N':  A * X = B  (No transpose) */
/*          = 'T':  A**T * X = B  (Transpose) */
/*          = 'C':  A**H * X = B  (Conjugate transpose = Transpose) */

/*  DIAG    (input) CHARACTER*1 */
/*          = 'N':  A is non-unit triangular; */
/*          = 'U':  A is unit triangular. */

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

/*  KD      (input) INTEGER */
/*          The number of superdiagonals or subdiagonals of the */
/*          triangular band matrix A.  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 upper or lower triangular band matrix A, stored in the */
/*          first kd+1 rows of AB.  The j-th column of A is stored */
/*          in the j-th column of the array AB as follows: */
/*          if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j; */
/*          if UPLO = 'L', AB(1+i-j,j)    = A(i,j) for j<=i<=min(n,j+kd). */
/*          If DIAG = 'U', the diagonal elements of A are not referenced */
/*          and are assumed to be 1. */

/*  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, if INFO = 0, 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 */
/*          > 0:  if INFO = i, the i-th diagonal element of A is zero, */
/*                indicating that the matrix is singular and the */
/*                solutions X have not been computed. */

/*  ===================================================================== */

/*     .. Parameters .. */
/*     .. */
/*     .. 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;
    nounit = lsame_(diag, "N");
    upper = lsame_(uplo, "U");
    if (! upper && ! lsame_(uplo, "L")) {
        *info = -1;
    } else if (! lsame_(trans, "N") && ! lsame_(trans, 
            "T") && ! lsame_(trans, "C")) {
        *info = -2;
    } else if (! nounit && ! lsame_(diag, "U")) {
        *info = -3;
    } else if (*n < 0) {
        *info = -4;
    } else if (*kd < 0) {
        *info = -5;
    } else if (*nrhs < 0) {
        *info = -6;
    } else if (*ldab < *kd + 1) {
        *info = -8;
    } else if (*ldb < max(1,*n)) {
        *info = -10;
    }
    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("STBTRS", &i__1);
        return 0;
    }

/*     Quick return if possible */

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

/*     Check for singularity. */

    if (nounit) {
        if (upper) {
            i__1 = *n;
            for (*info = 1; *info <= i__1; ++(*info)) {
                if (ab[*kd + 1 + *info * ab_dim1] == 0.f) {
                    return 0;
                }
/* L10: */
            }
        } else {
            i__1 = *n;
            for (*info = 1; *info <= i__1; ++(*info)) {
                if (ab[*info * ab_dim1 + 1] == 0.f) {
                    return 0;
                }
/* L20: */
            }
        }
    }
    *info = 0;

/*     Solve A * X = B  or  A' * X = B. */

    i__1 = *nrhs;
    for (j = 1; j <= i__1; ++j) {
        stbsv_(uplo, trans, diag, n, kd, &ab[ab_offset], ldab, &b[j * b_dim1 
                + 1], &c__1);
/* L30: */
    }

    return 0;

/*     End of STBTRS */

} /* stbtrs_ */