/*  -- 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 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 */

    static integer info;

    static doublereal 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   

    =======   

    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.   

    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      - 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.   

       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_("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);

			}

			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.) {

			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.) {

			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.) {

			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 DTRSV . */

} /* dtrsv_ */