/* -- translated by f2c (version 19940927).
You must link the resulting object file with the libraries:
-lf2c -lm (in that order)
*/
#include "f2c.h"
/* Subroutine */ int strsv_(char *uplo, char *trans, char *diag, integer *n,
real *a, integer *lda, real *x, integer *incx)
{
/* System generated locals */
integer a_dim1, a_offset, i__1, i__2;
/* Local variables */
static integer info;
static real temp;
static integer i, j;
extern logical lsame_(char *, char *);
static integer ix, jx, kx;
extern /* Subroutine */ int xerbla_(char *, integer *);
static logical nounit;
/* Purpose
=======
STRSV solves one of the systems of equations
A*x = b, or A'*x = b,
where b and x are n element vectors and A is an n by n unit, or
non-unit, upper or lower triangular matrix.
No test for singularity or near-singularity is included in this
routine. Such tests must be performed before calling this routine.
Parameters
==========
UPLO - CHARACTER*1.
On entry, UPLO specifies whether the matrix is an upper or
lower triangular matrix as follows:
UPLO = 'U' or 'u' A is an upper triangular matrix.
UPLO = 'L' or 'l' A is a lower triangular matrix.
Unchanged on exit.
TRANS - CHARACTER*1.
On entry, TRANS specifies the equations to be solved as
follows:
TRANS = 'N' or 'n' A*x = b.
TRANS = 'T' or 't' A'*x = b.
TRANS = 'C' or 'c' A'*x = b.
Unchanged on exit.
DIAG - CHARACTER*1.
On entry, DIAG specifies whether or not A is unit
triangular as follows:
DIAG = 'U' or 'u' A is assumed to be unit triangular.
DIAG = 'N' or 'n' A is not assumed to be unit
triangular.
Unchanged on exit.
N - INTEGER.
On entry, N specifies the order of the matrix A.
N must be at least zero.
Unchanged on exit.
A - REAL array of DIMENSION ( LDA, n ).
Before entry with UPLO = 'U' or 'u', the leading n by n
upper triangular part of the array A must contain the upper
triangular matrix and the strictly lower triangular part of
A is not referenced.
Before entry with UPLO = 'L' or 'l', the leading n by n
lower triangular part of the array A must contain the lower
triangular matrix and the strictly upper triangular part of
A is not referenced.
Note that when DIAG = 'U' or 'u', the diagonal elements of
A are not referenced either, but are assumed to be unity.
Unchanged on exit.
LDA - INTEGER.
On entry, LDA specifies the first dimension of A as declared
in the calling (sub) program. LDA must be at least
max( 1, n ).
Unchanged on exit.
X - REAL array of dimension at least
( 1 + ( n - 1 )*abs( INCX ) ).
Before entry, the incremented array X must contain the n
element right-hand side vector b. On exit, X is overwritten
with the solution vector x.
INCX - INTEGER.
On entry, INCX specifies the increment for the elements of
X. INCX must not be zero.
Unchanged on exit.
Level 2 Blas routine.
-- Written on 22-October-1986.
Jack Dongarra, Argonne National Lab.
Jeremy Du Croz, Nag Central Office.
Sven Hammarling, Nag Central Office.
Richard Hanson, Sandia National Labs.
Test the input parameters.
Parameter adjustments
Function Body */
#define X(I) x[(I)-1]
#define A(I,J) a[(I)-1 + ((J)-1)* ( *lda)]
info = 0;
if (! lsame_(uplo, "U") && ! lsame_(uplo, "L")) {
info = 1;
} else if (! lsame_(trans, "N") && ! lsame_(trans, "T") &&
! lsame_(trans, "C")) {
info = 2;
} else if (! lsame_(diag, "U") && ! lsame_(diag, "N")) {
info = 3;
} else if (*n < 0) {
info = 4;
} else if (*lda < max(1,*n)) {
info = 6;
} else if (*incx == 0) {
info = 8;
}
if (info != 0) {
xerbla_("STRSV ", &info);
return 0;
}
/* Quick return if possible. */
if (*n == 0) {
return 0;
}
nounit = lsame_(diag, "N");
/* Set up the start point in X if the increment is not unity. This
will be ( N - 1 )*INCX too small for descending loops. */
if (*incx <= 0) {
kx = 1 - (*n - 1) * *incx;
} else if (*incx != 1) {
kx = 1;
}
/* Start the operations. In this version the elements of A are
accessed sequentially with one pass through A. */
if (lsame_(trans, "N")) {
/* Form x := inv( A )*x. */
if (lsame_(uplo, "U")) {
if (*incx == 1) {
for (j = *n; j >= 1; --j) {
if (X(j) != 0.f) {
if (nounit) {
X(j) /= A(j,j);
}
temp = X(j);
for (i = j - 1; i >= 1; --i) {
X(i) -= temp * A(i,j);
/* L10: */
}
}
/* L20: */
}
} else {
jx = kx + (*n - 1) * *incx;
for (j = *n; j >= 1; --j) {
if (X(jx) != 0.f) {
if (nounit) {
X(jx) /= A(j,j);
}
temp = X(jx);
ix = jx;
for (i = j - 1; i >= 1; --i) {
ix -= *incx;
X(ix) -= temp * A(i,j);
/* L30: */
}
}
jx -= *incx;
/* L40: */
}
}
} else {
if (*incx == 1) {
i__1 = *n;
for (j = 1; j <= *n; ++j) {
if (X(j) != 0.f) {
if (nounit) {
X(j) /= A(j,j);
}
temp = X(j);
i__2 = *n;
for (i = j + 1; i <= *n; ++i) {
X(i) -= temp * A(i,j);
/* L50: */
}
}
/* L60: */
}
} else {
jx = kx;
i__1 = *n;
for (j = 1; j <= *n; ++j) {
if (X(jx) != 0.f) {
if (nounit) {
X(jx) /= A(j,j);
}
temp = X(jx);
ix = jx;
i__2 = *n;
for (i = j + 1; i <= *n; ++i) {
ix += *incx;
X(ix) -= temp * A(i,j);
/* L70: */
}
}
jx += *incx;
/* L80: */
}
}
}
} else {
/* Form x := inv( A' )*x. */
if (lsame_(uplo, "U")) {
if (*incx == 1) {
i__1 = *n;
for (j = 1; j <= *n; ++j) {
temp = X(j);
i__2 = j - 1;
for (i = 1; i <= j-1; ++i) {
temp -= A(i,j) * X(i);
/* L90: */
}
if (nounit) {
temp /= A(j,j);
}
X(j) = temp;
/* L100: */
}
} else {
jx = kx;
i__1 = *n;
for (j = 1; j <= *n; ++j) {
temp = X(jx);
ix = kx;
i__2 = j - 1;
for (i = 1; i <= j-1; ++i) {
temp -= A(i,j) * X(ix);
ix += *incx;
/* L110: */
}
if (nounit) {
temp /= A(j,j);
}
X(jx) = temp;
jx += *incx;
/* L120: */
}
}
} else {
if (*incx == 1) {
for (j = *n; j >= 1; --j) {
temp = X(j);
i__1 = j + 1;
for (i = *n; i >= j+1; --i) {
temp -= A(i,j) * X(i);
/* L130: */
}
if (nounit) {
temp /= A(j,j);
}
X(j) = temp;
/* L140: */
}
} else {
kx += (*n - 1) * *incx;
jx = kx;
for (j = *n; j >= 1; --j) {
temp = X(jx);
ix = kx;
i__1 = j + 1;
for (i = *n; i >= j+1; --i) {
temp -= A(i,j) * X(ix);
ix -= *incx;
/* L150: */
}
if (nounit) {
temp /= A(j,j);
}
X(jx) = temp;
jx -= *incx;
/* L160: */
}
}
}
}
return 0;
/* End of STRSV . */
} /* strsv_ */