#include "f2c.h"
#include "blaswrap.h"

/* Subroutine */ int dtrsv_(char *uplo, char *trans, char *diag, integer *n, 
	doublereal *a, integer *lda, doublereal *x, integer *incx)
{
    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2;

    /* Local variables */
    integer i__, j, ix, jx, kx, info;
    doublereal temp;
    extern logical lsame_(char *, char *);
    extern /* Subroutine */ int xerbla_(char *, integer *);
    logical nounit;

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */

/*  Purpose */
/*  ======= */

/*  DTRSV  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. */

/*  Arguments */
/*  ========== */

/*  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      - DOUBLE PRECISION 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      - DOUBLE PRECISION 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. */


/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. External Functions .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */
/*     .. Intrinsic Functions .. */
/*     .. */

/*     Test the input parameters. */

    /* Parameter adjustments */
    a_dim1 = *lda;
    a_offset = 1 + a_dim1;
    a -= a_offset;
    --x;

    /* Function Body */
    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_("DTRSV ", &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.) {
			if (nounit) {
			    x[j] /= a[j + j * a_dim1];
			}
			temp = x[j];
			for (i__ = j - 1; i__ >= 1; --i__) {
			    x[i__] -= temp * a[i__ + j * a_dim1];
/* L10: */
			}
		    }
/* L20: */
		}
	    } else {
		jx = kx + (*n - 1) * *incx;
		for (j = *n; j >= 1; --j) {
		    if (x[jx] != 0.) {
			if (nounit) {
			    x[jx] /= a[j + j * a_dim1];
			}
			temp = x[jx];
			ix = jx;
			for (i__ = j - 1; i__ >= 1; --i__) {
			    ix -= *incx;
			    x[ix] -= temp * a[i__ + j * a_dim1];
/* L30: */
			}
		    }
		    jx -= *incx;
/* L40: */
		}
	    }
	} else {
	    if (*incx == 1) {
		i__1 = *n;
		for (j = 1; j <= i__1; ++j) {
		    if (x[j] != 0.) {
			if (nounit) {
			    x[j] /= a[j + j * a_dim1];
			}
			temp = x[j];
			i__2 = *n;
			for (i__ = j + 1; i__ <= i__2; ++i__) {
			    x[i__] -= temp * a[i__ + j * a_dim1];
/* L50: */
			}
		    }
/* L60: */
		}
	    } else {
		jx = kx;
		i__1 = *n;
		for (j = 1; j <= i__1; ++j) {
		    if (x[jx] != 0.) {
			if (nounit) {
			    x[jx] /= a[j + j * a_dim1];
			}
			temp = x[jx];
			ix = jx;
			i__2 = *n;
			for (i__ = j + 1; i__ <= i__2; ++i__) {
			    ix += *incx;
			    x[ix] -= temp * a[i__ + j * a_dim1];
/* L70: */
			}
		    }
		    jx += *incx;
/* L80: */
		}
	    }
	}
    } else {

/*        Form  x := inv( A' )*x. */

	if (lsame_(uplo, "U")) {
	    if (*incx == 1) {
		i__1 = *n;
		for (j = 1; j <= i__1; ++j) {
		    temp = x[j];
		    i__2 = j - 1;
		    for (i__ = 1; i__ <= i__2; ++i__) {
			temp -= a[i__ + j * a_dim1] * x[i__];
/* L90: */
		    }
		    if (nounit) {
			temp /= a[j + j * a_dim1];
		    }
		    x[j] = temp;
/* L100: */
		}
	    } else {
		jx = kx;
		i__1 = *n;
		for (j = 1; j <= i__1; ++j) {
		    temp = x[jx];
		    ix = kx;
		    i__2 = j - 1;
		    for (i__ = 1; i__ <= i__2; ++i__) {
			temp -= a[i__ + j * a_dim1] * x[ix];
			ix += *incx;
/* L110: */
		    }
		    if (nounit) {
			temp /= a[j + j * a_dim1];
		    }
		    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__ >= i__1; --i__) {
			temp -= a[i__ + j * a_dim1] * x[i__];
/* L130: */
		    }
		    if (nounit) {
			temp /= a[j + j * a_dim1];
		    }
		    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__ >= i__1; --i__) {
			temp -= a[i__ + j * a_dim1] * x[ix];
			ix -= *incx;
/* L150: */
		    }
		    if (nounit) {
			temp /= a[j + j * a_dim1];
		    }
		    x[jx] = temp;
		    jx -= *incx;
/* L160: */
		}
	    }
	}
    }

    return 0;

/*     End of DTRSV . */

} /* dtrsv_ */