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/* dgtts2.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 dgtts2_(integer *itrans, integer *n, integer *nrhs,
doublereal *dl, doublereal *d__, doublereal *du, doublereal *du2,
integer *ipiv, doublereal *b, integer *ldb)
{
/* System generated locals */
integer b_dim1, b_offset, i__1, i__2;
/* Local variables */
integer i__, j, ip;
doublereal temp;
/* -- LAPACK auxiliary routine (version 3.2) -- */
/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/* November 2006 */
/* .. Scalar Arguments .. */
/* .. */
/* .. Array Arguments .. */
/* .. */
/* Purpose */
/* ======= */
/* DGTTS2 solves one of the systems of equations */
/* A*X = B or A'*X = B, */
/* with a tridiagonal matrix A using the LU factorization computed */
/* by DGTTRF. */
/* Arguments */
/* ========= */
/* ITRANS (input) INTEGER */
/* Specifies the form of the system of equations. */
/* = 0: A * X = B (No transpose) */
/* = 1: A'* X = B (Transpose) */
/* = 2: A'* X = B (Conjugate transpose = Transpose) */
/* N (input) INTEGER */
/* The order of the matrix A. */
/* NRHS (input) INTEGER */
/* The number of right hand sides, i.e., the number of columns */
/* of the matrix B. NRHS >= 0. */
/* DL (input) DOUBLE PRECISION array, dimension (N-1) */
/* The (n-1) multipliers that define the matrix L from the */
/* LU factorization of A. */
/* D (input) DOUBLE PRECISION array, dimension (N) */
/* The n diagonal elements of the upper triangular matrix U from */
/* the LU factorization of A. */
/* DU (input) DOUBLE PRECISION array, dimension (N-1) */
/* The (n-1) elements of the first super-diagonal of U. */
/* DU2 (input) DOUBLE PRECISION array, dimension (N-2) */
/* The (n-2) elements of the second super-diagonal of U. */
/* IPIV (input) INTEGER array, dimension (N) */
/* The pivot indices; for 1 <= i <= n, row i of the matrix was */
/* interchanged with row IPIV(i). IPIV(i) will always be either */
/* i or i+1; IPIV(i) = i indicates a row interchange was not */
/* required. */
/* B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS) */
/* On entry, the matrix of right hand side vectors B. */
/* On exit, B is overwritten by the solution vectors X. */
/* LDB (input) INTEGER */
/* The leading dimension of the array B. LDB >= max(1,N). */
/* ===================================================================== */
/* .. Local Scalars .. */
/* .. */
/* .. Executable Statements .. */
/* Quick return if possible */
/* Parameter adjustments */
--dl;
--d__;
--du;
--du2;
--ipiv;
b_dim1 = *ldb;
b_offset = 1 + b_dim1;
b -= b_offset;
/* Function Body */
if (*n == 0 || *nrhs == 0) {
return 0;
}
if (*itrans == 0) {
/* Solve A*X = B using the LU factorization of A, */
/* overwriting each right hand side vector with its solution. */
if (*nrhs <= 1) {
j = 1;
L10:
/* Solve L*x = b. */
i__1 = *n - 1;
for (i__ = 1; i__ <= i__1; ++i__) {
ip = ipiv[i__];
temp = b[i__ + 1 - ip + i__ + j * b_dim1] - dl[i__] * b[ip +
j * b_dim1];
b[i__ + j * b_dim1] = b[ip + j * b_dim1];
b[i__ + 1 + j * b_dim1] = temp;
/* L20: */
}
/* Solve U*x = b. */
b[*n + j * b_dim1] /= d__[*n];
if (*n > 1) {
b[*n - 1 + j * b_dim1] = (b[*n - 1 + j * b_dim1] - du[*n - 1]
* b[*n + j * b_dim1]) / d__[*n - 1];
}
for (i__ = *n - 2; i__ >= 1; --i__) {
b[i__ + j * b_dim1] = (b[i__ + j * b_dim1] - du[i__] * b[i__
+ 1 + j * b_dim1] - du2[i__] * b[i__ + 2 + j * b_dim1]
) / d__[i__];
/* L30: */
}
if (j < *nrhs) {
++j;
goto L10;
}
} else {
i__1 = *nrhs;
for (j = 1; j <= i__1; ++j) {
/* Solve L*x = b. */
i__2 = *n - 1;
for (i__ = 1; i__ <= i__2; ++i__) {
if (ipiv[i__] == i__) {
b[i__ + 1 + j * b_dim1] -= dl[i__] * b[i__ + j *
b_dim1];
} else {
temp = b[i__ + j * b_dim1];
b[i__ + j * b_dim1] = b[i__ + 1 + j * b_dim1];
b[i__ + 1 + j * b_dim1] = temp - dl[i__] * b[i__ + j *
b_dim1];
}
/* L40: */
}
/* Solve U*x = b. */
b[*n + j * b_dim1] /= d__[*n];
if (*n > 1) {
b[*n - 1 + j * b_dim1] = (b[*n - 1 + j * b_dim1] - du[*n
- 1] * b[*n + j * b_dim1]) / d__[*n - 1];
}
for (i__ = *n - 2; i__ >= 1; --i__) {
b[i__ + j * b_dim1] = (b[i__ + j * b_dim1] - du[i__] * b[
i__ + 1 + j * b_dim1] - du2[i__] * b[i__ + 2 + j *
b_dim1]) / d__[i__];
/* L50: */
}
/* L60: */
}
}
} else {
/* Solve A' * X = B. */
if (*nrhs <= 1) {
/* Solve U'*x = b. */
j = 1;
L70:
b[j * b_dim1 + 1] /= d__[1];
if (*n > 1) {
b[j * b_dim1 + 2] = (b[j * b_dim1 + 2] - du[1] * b[j * b_dim1
+ 1]) / d__[2];
}
i__1 = *n;
for (i__ = 3; i__ <= i__1; ++i__) {
b[i__ + j * b_dim1] = (b[i__ + j * b_dim1] - du[i__ - 1] * b[
i__ - 1 + j * b_dim1] - du2[i__ - 2] * b[i__ - 2 + j *
b_dim1]) / d__[i__];
/* L80: */
}
/* Solve L'*x = b. */
for (i__ = *n - 1; i__ >= 1; --i__) {
ip = ipiv[i__];
temp = b[i__ + j * b_dim1] - dl[i__] * b[i__ + 1 + j * b_dim1]
;
b[i__ + j * b_dim1] = b[ip + j * b_dim1];
b[ip + j * b_dim1] = temp;
/* L90: */
}
if (j < *nrhs) {
++j;
goto L70;
}
} else {
i__1 = *nrhs;
for (j = 1; j <= i__1; ++j) {
/* Solve U'*x = b. */
b[j * b_dim1 + 1] /= d__[1];
if (*n > 1) {
b[j * b_dim1 + 2] = (b[j * b_dim1 + 2] - du[1] * b[j *
b_dim1 + 1]) / d__[2];
}
i__2 = *n;
for (i__ = 3; i__ <= i__2; ++i__) {
b[i__ + j * b_dim1] = (b[i__ + j * b_dim1] - du[i__ - 1] *
b[i__ - 1 + j * b_dim1] - du2[i__ - 2] * b[i__ -
2 + j * b_dim1]) / d__[i__];
/* L100: */
}
for (i__ = *n - 1; i__ >= 1; --i__) {
if (ipiv[i__] == i__) {
b[i__ + j * b_dim1] -= dl[i__] * b[i__ + 1 + j *
b_dim1];
} else {
temp = b[i__ + 1 + j * b_dim1];
b[i__ + 1 + j * b_dim1] = b[i__ + j * b_dim1] - dl[
i__] * temp;
b[i__ + j * b_dim1] = temp;
}
/* L110: */
}
/* L120: */
}
}
}
/* End of DGTTS2 */
return 0;
} /* dgtts2_ */
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