/* dgtsv.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 dgtsv_(integer *n, integer *nrhs, doublereal *dl,
doublereal *d__, doublereal *du, doublereal *b, integer *ldb, integer
*info)
{
/* System generated locals */
integer b_dim1, b_offset, i__1, i__2;
doublereal d__1, d__2;
/* Local variables */
integer i__, j;
doublereal fact, temp;
extern /* Subroutine */ int 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 */
/* ======= */
/* DGTSV solves the equation */
/* A*X = B, */
/* where A is an n by n tridiagonal matrix, by Gaussian elimination with */
/* partial pivoting. */
/* Note that the equation A'*X = B may be solved by interchanging the */
/* order of the arguments DU and DL. */
/* Arguments */
/* ========= */
/* N (input) INTEGER */
/* The order of the matrix A. N >= 0. */
/* NRHS (input) INTEGER */
/* The number of right hand sides, i.e., the number of columns */
/* of the matrix B. NRHS >= 0. */
/* DL (input/output) DOUBLE PRECISION array, dimension (N-1) */
/* On entry, DL must contain the (n-1) sub-diagonal elements of */
/* A. */
/* On exit, DL is overwritten by the (n-2) elements of the */
/* second super-diagonal of the upper triangular matrix U from */
/* the LU factorization of A, in DL(1), ..., DL(n-2). */
/* D (input/output) DOUBLE PRECISION array, dimension (N) */
/* On entry, D must contain the diagonal elements of A. */
/* On exit, D is overwritten by the n diagonal elements of U. */
/* DU (input/output) DOUBLE PRECISION array, dimension (N-1) */
/* On entry, DU must contain the (n-1) super-diagonal elements */
/* of A. */
/* On exit, DU is overwritten by the (n-1) elements of the first */
/* super-diagonal of U. */
/* B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS) */
/* On entry, the N by NRHS matrix of right hand side matrix B. */
/* On exit, if INFO = 0, the N by NRHS 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, U(i,i) is exactly zero, and the solution */
/* has not been computed. The factorization has not been */
/* completed unless i = N. */
/* ===================================================================== */
/* .. Parameters .. */
/* .. */
/* .. Local Scalars .. */
/* .. */
/* .. Intrinsic Functions .. */
/* .. */
/* .. External Subroutines .. */
/* .. */
/* .. Executable Statements .. */
/* Parameter adjustments */
--dl;
--d__;
--du;
b_dim1 = *ldb;
b_offset = 1 + b_dim1;
b -= b_offset;
/* Function Body */
*info = 0;
if (*n < 0) {
*info = -1;
} else if (*nrhs < 0) {
*info = -2;
} else if (*ldb < max(1,*n)) {
*info = -7;
}
if (*info != 0) {
i__1 = -(*info);
xerbla_("DGTSV ", &i__1);
return 0;
}
if (*n == 0) {
return 0;
}
if (*nrhs == 1) {
i__1 = *n - 2;
for (i__ = 1; i__ <= i__1; ++i__) {
if ((d__1 = d__[i__], abs(d__1)) >= (d__2 = dl[i__], abs(d__2))) {
/* No row interchange required */
if (d__[i__] != 0.) {
fact = dl[i__] / d__[i__];
d__[i__ + 1] -= fact * du[i__];
b[i__ + 1 + b_dim1] -= fact * b[i__ + b_dim1];
} else {
*info = i__;
return 0;
}
dl[i__] = 0.;
} else {
/* Interchange rows I and I+1 */
fact = d__[i__] / dl[i__];
d__[i__] = dl[i__];
temp = d__[i__ + 1];
d__[i__ + 1] = du[i__] - fact * temp;
dl[i__] = du[i__ + 1];
du[i__ + 1] = -fact * dl[i__];
du[i__] = temp;
temp = b[i__ + b_dim1];
b[i__ + b_dim1] = b[i__ + 1 + b_dim1];
b[i__ + 1 + b_dim1] = temp - fact * b[i__ + 1 + b_dim1];
}
/* L10: */
}
if (*n > 1) {
i__ = *n - 1;
if ((d__1 = d__[i__], abs(d__1)) >= (d__2 = dl[i__], abs(d__2))) {
if (d__[i__] != 0.) {
fact = dl[i__] / d__[i__];
d__[i__ + 1] -= fact * du[i__];
b[i__ + 1 + b_dim1] -= fact * b[i__ + b_dim1];
} else {
*info = i__;
return 0;
}
} else {
fact = d__[i__] / dl[i__];
d__[i__] = dl[i__];
temp = d__[i__ + 1];
d__[i__ + 1] = du[i__] - fact * temp;
du[i__] = temp;
temp = b[i__ + b_dim1];
b[i__ + b_dim1] = b[i__ + 1 + b_dim1];
b[i__ + 1 + b_dim1] = temp - fact * b[i__ + 1 + b_dim1];
}
}
if (d__[*n] == 0.) {
*info = *n;
return 0;
}
} else {
i__1 = *n - 2;
for (i__ = 1; i__ <= i__1; ++i__) {
if ((d__1 = d__[i__], abs(d__1)) >= (d__2 = dl[i__], abs(d__2))) {
/* No row interchange required */
if (d__[i__] != 0.) {
fact = dl[i__] / d__[i__];
d__[i__ + 1] -= fact * du[i__];
i__2 = *nrhs;
for (j = 1; j <= i__2; ++j) {
b[i__ + 1 + j * b_dim1] -= fact * b[i__ + j * b_dim1];
/* L20: */
}
} else {
*info = i__;
return 0;
}
dl[i__] = 0.;
} else {
/* Interchange rows I and I+1 */
fact = d__[i__] / dl[i__];
d__[i__] = dl[i__];
temp = d__[i__ + 1];
d__[i__ + 1] = du[i__] - fact * temp;
dl[i__] = du[i__ + 1];
du[i__ + 1] = -fact * dl[i__];
du[i__] = temp;
i__2 = *nrhs;
for (j = 1; j <= i__2; ++j) {
temp = b[i__ + j * b_dim1];
b[i__ + j * b_dim1] = b[i__ + 1 + j * b_dim1];
b[i__ + 1 + j * b_dim1] = temp - fact * b[i__ + 1 + j *
b_dim1];
/* L30: */
}
}
/* L40: */
}
if (*n > 1) {
i__ = *n - 1;
if ((d__1 = d__[i__], abs(d__1)) >= (d__2 = dl[i__], abs(d__2))) {
if (d__[i__] != 0.) {
fact = dl[i__] / d__[i__];
d__[i__ + 1] -= fact * du[i__];
i__1 = *nrhs;
for (j = 1; j <= i__1; ++j) {
b[i__ + 1 + j * b_dim1] -= fact * b[i__ + j * b_dim1];
/* L50: */
}
} else {
*info = i__;
return 0;
}
} else {
fact = d__[i__] / dl[i__];
d__[i__] = dl[i__];
temp = d__[i__ + 1];
d__[i__ + 1] = du[i__] - fact * temp;
du[i__] = temp;
i__1 = *nrhs;
for (j = 1; j <= i__1; ++j) {
temp = b[i__ + j * b_dim1];
b[i__ + j * b_dim1] = b[i__ + 1 + j * b_dim1];
b[i__ + 1 + j * b_dim1] = temp - fact * b[i__ + 1 + j *
b_dim1];
/* L60: */
}
}
}
if (d__[*n] == 0.) {
*info = *n;
return 0;
}
}
/* Back solve with the matrix U from the factorization. */
if (*nrhs <= 2) {
j = 1;
L70:
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] - dl[i__] * b[i__ + 2 + j * b_dim1]) / d__[
i__];
/* L80: */
}
if (j < *nrhs) {
++j;
goto L70;
}
} else {
i__1 = *nrhs;
for (j = 1; j <= i__1; ++j) {
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] - dl[i__] * b[i__ + 2 + j * b_dim1])
/ d__[i__];
/* L90: */
}
/* L100: */
}
}
return 0;
/* End of DGTSV */
} /* dgtsv_ */
