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

/* Subroutine */ int sgtsv_(integer *n, integer *nrhs, real *dl, real *d__, 
	real *du, real *b, integer *ldb, integer *info)
{
/*  -- LAPACK routine (version 3.1) --   
       Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..   
       November 2006   


    Purpose   
    =======   

    SGTSV  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) REAL 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) REAL 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) REAL 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) REAL 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.   

    =====================================================================   


       Parameter adjustments */
    /* System generated locals */
    integer b_dim1, b_offset, i__1, i__2;
    real r__1, r__2;
    /* Local variables */
    static integer i__, j;
    static real fact, temp;
    extern /* Subroutine */ int xerbla_(char *, integer *);

    --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_("SGTSV ", &i__1);
	return 0;
    }

    if (*n == 0) {
	return 0;
    }

    if (*nrhs == 1) {
	i__1 = *n - 2;
	for (i__ = 1; i__ <= i__1; ++i__) {
	    if ((r__1 = d__[i__], dabs(r__1)) >= (r__2 = dl[i__], dabs(r__2)))
		     {

/*              No row interchange required */

		if (d__[i__] != 0.f) {
		    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.f;
	    } 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 ((r__1 = d__[i__], dabs(r__1)) >= (r__2 = dl[i__], dabs(r__2)))
		     {
		if (d__[i__] != 0.f) {
		    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.f) {
	    *info = *n;
	    return 0;
	}
    } else {
	i__1 = *n - 2;
	for (i__ = 1; i__ <= i__1; ++i__) {
	    if ((r__1 = d__[i__], dabs(r__1)) >= (r__2 = dl[i__], dabs(r__2)))
		     {

/*              No row interchange required */

		if (d__[i__] != 0.f) {
		    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.f;
	    } 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 ((r__1 = d__[i__], dabs(r__1)) >= (r__2 = dl[i__], dabs(r__2)))
		     {
		if (d__[i__] != 0.f) {
		    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.f) {
	    *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 SGTSV */

} /* sgtsv_ */