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/* dtptri.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 dtptri_(char *uplo, char *diag, integer *n, doublereal *
ap, integer *info)
{
/* System generated locals */
integer i__1, i__2;
/* Local variables */
integer j, jc, jj;
doublereal ajj;
extern /* Subroutine */ int dscal_(integer *, doublereal *, doublereal *,
integer *);
extern logical lsame_(char *, char *);
extern /* Subroutine */ int dtpmv_(char *, char *, char *, integer *,
doublereal *, doublereal *, integer *);
logical upper;
extern /* Subroutine */ int xerbla_(char *, integer *);
integer jclast;
logical nounit;
/* -- LAPACK routine (version 3.2) -- */
/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/* November 2006 */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* Purpose */
/* ======= */
/* DTPTRI computes the inverse of a real upper or lower triangular */
/* matrix A stored in packed format. */
/* Arguments */
/* ========= */
/* 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. */
/* AP (input/output) DOUBLE PRECISION array, dimension (N*(N+1)/2) */
/* On entry, the upper or lower triangular matrix A, stored */
/* columnwise in a linear array. The j-th column of A is stored */
/* in the array AP as follows: */
/* if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; */
/* if UPLO = 'L', AP(i + (j-1)*((2*n-j)/2) = A(i,j) for j<=i<=n. */
/* See below for further details. */
/* On exit, the (triangular) inverse of the original matrix, in */
/* the same packed storage format. */
/* INFO (output) INTEGER */
/* = 0: successful exit */
/* < 0: if INFO = -i, the i-th argument had an illegal value */
/* > 0: if INFO = i, A(i,i) is exactly zero. The triangular */
/* matrix is singular and its inverse can not be computed. */
/* Further Details */
/* =============== */
/* A triangular matrix A can be transferred to packed storage using one */
/* of the following program segments: */
/* UPLO = 'U': UPLO = 'L': */
/* JC = 1 JC = 1 */
/* DO 2 J = 1, N DO 2 J = 1, N */
/* DO 1 I = 1, J DO 1 I = J, N */
/* AP(JC+I-1) = A(I,J) AP(JC+I-J) = A(I,J) */
/* 1 CONTINUE 1 CONTINUE */
/* JC = JC + J JC = JC + N - J + 1 */
/* 2 CONTINUE 2 CONTINUE */
/* ===================================================================== */
/* .. Parameters .. */
/* .. */
/* .. Local Scalars .. */
/* .. */
/* .. External Functions .. */
/* .. */
/* .. External Subroutines .. */
/* .. */
/* .. Executable Statements .. */
/* Test the input parameters. */
/* Parameter adjustments */
--ap;
/* Function Body */
*info = 0;
upper = lsame_(uplo, "U");
nounit = lsame_(diag, "N");
if (! upper && ! lsame_(uplo, "L")) {
*info = -1;
} else if (! nounit && ! lsame_(diag, "U")) {
*info = -2;
} else if (*n < 0) {
*info = -3;
}
if (*info != 0) {
i__1 = -(*info);
xerbla_("DTPTRI", &i__1);
return 0;
}
/* Check for singularity if non-unit. */
if (nounit) {
if (upper) {
jj = 0;
i__1 = *n;
for (*info = 1; *info <= i__1; ++(*info)) {
jj += *info;
if (ap[jj] == 0.) {
return 0;
}
/* L10: */
}
} else {
jj = 1;
i__1 = *n;
for (*info = 1; *info <= i__1; ++(*info)) {
if (ap[jj] == 0.) {
return 0;
}
jj = jj + *n - *info + 1;
/* L20: */
}
}
*info = 0;
}
if (upper) {
/* Compute inverse of upper triangular matrix. */
jc = 1;
i__1 = *n;
for (j = 1; j <= i__1; ++j) {
if (nounit) {
ap[jc + j - 1] = 1. / ap[jc + j - 1];
ajj = -ap[jc + j - 1];
} else {
ajj = -1.;
}
/* Compute elements 1:j-1 of j-th column. */
i__2 = j - 1;
dtpmv_("Upper", "No transpose", diag, &i__2, &ap[1], &ap[jc], &
c__1);
i__2 = j - 1;
dscal_(&i__2, &ajj, &ap[jc], &c__1);
jc += j;
/* L30: */
}
} else {
/* Compute inverse of lower triangular matrix. */
jc = *n * (*n + 1) / 2;
for (j = *n; j >= 1; --j) {
if (nounit) {
ap[jc] = 1. / ap[jc];
ajj = -ap[jc];
} else {
ajj = -1.;
}
if (j < *n) {
/* Compute elements j+1:n of j-th column. */
i__1 = *n - j;
dtpmv_("Lower", "No transpose", diag, &i__1, &ap[jclast], &ap[
jc + 1], &c__1);
i__1 = *n - j;
dscal_(&i__1, &ajj, &ap[jc + 1], &c__1);
}
jclast = jc;
jc = jc - *n + j - 2;
/* L40: */
}
}
return 0;
/* End of DTPTRI */
} /* dtptri_ */
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