#include "blaswrap.h"
#include "f2c.h"
/* Subroutine */ int ctbcon_(char *norm, char *uplo, char *diag, integer *n,
integer *kd, complex *ab, integer *ldab, real *rcond, complex *work,
real *rwork, integer *info)
{
/* -- LAPACK routine (version 3.0) --
Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
Courant Institute, Argonne National Lab, and Rice University
March 31, 1993
Purpose
=======
CTBCON estimates the reciprocal of the condition number of a
triangular band matrix A, in either the 1-norm or the infinity-norm.
The norm of A is computed and an estimate is obtained for
norm(inv(A)), then the reciprocal of the condition number is
computed as
RCOND = 1 / ( norm(A) * norm(inv(A)) ).
Arguments
=========
NORM (input) CHARACTER*1
Specifies whether the 1-norm condition number or the
infinity-norm condition number is required:
= '1' or 'O': 1-norm;
= 'I': Infinity-norm.
UPLO (input) CHARACTER*1
= 'U': A is upper triangular;
= 'L': A is lower triangular.
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.
AB (input) COMPLEX array, dimension (LDAB,N)
The upper or lower triangular band matrix A, stored in the
first kd+1 rows of the array. 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.
RCOND (output) REAL
The reciprocal of the condition number of the matrix A,
computed as RCOND = 1/(norm(A) * norm(inv(A))).
WORK (workspace) COMPLEX array, dimension (2*N)
RWORK (workspace) REAL array, dimension (N)
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
=====================================================================
Test the input parameters.
Parameter adjustments */
/* Table of constant values */
static integer c__1 = 1;
/* System generated locals */
integer ab_dim1, ab_offset, i__1;
real r__1, r__2;
/* Builtin functions */
double r_imag(complex *);
/* Local variables */
static integer kase, kase1;
static real scale;
extern logical lsame_(char *, char *);
static real anorm;
static logical upper;
static real xnorm;
extern /* Subroutine */ int clacon_(integer *, complex *, complex *, real
*, integer *);
static integer ix;
extern integer icamax_(integer *, complex *, integer *);
extern doublereal clantb_(char *, char *, char *, integer *, integer *,
complex *, integer *, real *), slamch_(
char *);
extern /* Subroutine */ int clatbs_(char *, char *, char *, char *,
integer *, integer *, complex *, integer *, complex *, real *,
real *, integer *), xerbla_(char *
, integer *);
static real ainvnm;
extern /* Subroutine */ int csrscl_(integer *, real *, complex *, integer
*);
static logical onenrm;
static char normin[1];
static real smlnum;
static logical nounit;
ab_dim1 = *ldab;
ab_offset = 1 + ab_dim1 * 1;
ab -= ab_offset;
--work;
--rwork;
/* Function Body */
*info = 0;
upper = lsame_(uplo, "U");
onenrm = *(unsigned char *)norm == '1' || lsame_(norm, "O");
nounit = lsame_(diag, "N");
if (! onenrm && ! lsame_(norm, "I")) {
*info = -1;
} else if (! upper && ! lsame_(uplo, "L")) {
*info = -2;
} else if (! nounit && ! lsame_(diag, "U")) {
*info = -3;
} else if (*n < 0) {
*info = -4;
} else if (*kd < 0) {
*info = -5;
} else if (*ldab < *kd + 1) {
*info = -7;
}
if (*info != 0) {
i__1 = -(*info);
xerbla_("CTBCON", &i__1);
return 0;
}
/* Quick return if possible */
if (*n == 0) {
*rcond = 1.f;
return 0;
}
*rcond = 0.f;
smlnum = slamch_("Safe minimum") * (real) max(*n,1);
/* Compute the 1-norm of the triangular matrix A or A'. */
anorm = clantb_(norm, uplo, diag, n, kd, &ab[ab_offset], ldab, &rwork[1]);
/* Continue only if ANORM > 0. */
if (anorm > 0.f) {
/* Estimate the 1-norm of the inverse of A. */
ainvnm = 0.f;
*(unsigned char *)normin = 'N';
if (onenrm) {
kase1 = 1;
} else {
kase1 = 2;
}
kase = 0;
L10:
clacon_(n, &work[*n + 1], &work[1], &ainvnm, &kase);
if (kase != 0) {
if (kase == kase1) {
/* Multiply by inv(A). */
clatbs_(uplo, "No transpose", diag, normin, n, kd, &ab[
ab_offset], ldab, &work[1], &scale, &rwork[1], info);
} else {
/* Multiply by inv(A'). */
clatbs_(uplo, "Conjugate transpose", diag, normin, n, kd, &ab[
ab_offset], ldab, &work[1], &scale, &rwork[1], info);
}
*(unsigned char *)normin = 'Y';
/* Multiply by 1/SCALE if doing so will not cause overflow. */
if (scale != 1.f) {
ix = icamax_(n, &work[1], &c__1);
i__1 = ix;
xnorm = (r__1 = work[i__1].r, dabs(r__1)) + (r__2 = r_imag(&
work[ix]), dabs(r__2));
if (scale < xnorm * smlnum || scale == 0.f) {
goto L20;
}
csrscl_(n, &scale, &work[1], &c__1);
}
goto L10;
}
/* Compute the estimate of the reciprocal condition number. */
if (ainvnm != 0.f) {
*rcond = 1.f / anorm / ainvnm;
}
}
L20:
return 0;
/* End of CTBCON */
} /* ctbcon_ */