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

/* Subroutine */ int cgttrf_(integer *n, complex *dl, complex *d__, complex *
	du, complex *du2, integer *ipiv, integer *info)
{
/*  -- LAPACK routine (version 3.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       June 30, 1999   


    Purpose   
    =======   

    CGTTRF computes an LU factorization of a complex tridiagonal matrix A   
    using elimination with partial pivoting and row interchanges.   

    The factorization has the form   
       A = L * U   
    where L is a product of permutation and unit lower bidiagonal   
    matrices and U is upper triangular with nonzeros in only the main   
    diagonal and first two superdiagonals.   

    Arguments   
    =========   

    N       (input) INTEGER   
            The order of the matrix A.   

    DL      (input/output) COMPLEX 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-1) multipliers that   
            define the matrix L from the LU factorization of A.   

    D       (input/output) COMPLEX array, dimension (N)   
            On entry, D must contain the diagonal elements of A.   

            On exit, D is overwritten by the n diagonal elements of the   
            upper triangular matrix U from the LU factorization of A.   

    DU      (input/output) COMPLEX 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.   

    DU2     (output) COMPLEX array, dimension (N-2)   
            On exit, DU2 is overwritten by the (n-2) elements of the   
            second super-diagonal of U.   

    IPIV    (output) INTEGER array, dimension (N)   
            The pivot indices; for 1 <= i <= n, row i of the matrix was   
            interchanged with row IPIV(i).  IPIV(i) will always be either   
            i or i+1; IPIV(i) = i indicates a row interchange was not   
            required.   

    INFO    (output) INTEGER   
            = 0:  successful exit   
            < 0:  if INFO = -k, the k-th argument had an illegal value   
            > 0:  if INFO = k, U(k,k) is exactly zero. The factorization   
                  has been completed, but the factor U is exactly   
                  singular, and division by zero will occur if it is used   
                  to solve a system of equations.   

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


       Parameter adjustments */
    /* System generated locals */
    integer i__1, i__2, i__3, i__4;
    real r__1, r__2, r__3, r__4;
    complex q__1, q__2;
    /* Builtin functions */
    double r_imag(complex *);
    void c_div(complex *, complex *, complex *);
    /* Local variables */
    static complex fact, temp;
    static integer i__;
    extern /* Subroutine */ int xerbla_(char *, integer *);

    --ipiv;
    --du2;
    --du;
    --d__;
    --dl;

    /* Function Body */
    *info = 0;
    if (*n < 0) {
	*info = -1;
	i__1 = -(*info);
	xerbla_("CGTTRF", &i__1);
	return 0;
    }

/*     Quick return if possible */

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

/*     Initialize IPIV(i) = i and DU2(i) = 0 */

    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
	ipiv[i__] = i__;
/* L10: */
    }
    i__1 = *n - 2;
    for (i__ = 1; i__ <= i__1; ++i__) {
	i__2 = i__;
	du2[i__2].r = 0.f, du2[i__2].i = 0.f;
/* L20: */
    }

    i__1 = *n - 2;
    for (i__ = 1; i__ <= i__1; ++i__) {
	i__2 = i__;
	i__3 = i__;
	if ((r__1 = d__[i__2].r, dabs(r__1)) + (r__2 = r_imag(&d__[i__]), 
		dabs(r__2)) >= (r__3 = dl[i__3].r, dabs(r__3)) + (r__4 = 
		r_imag(&dl[i__]), dabs(r__4))) {

/*           No row interchange required, eliminate DL(I) */

	    i__2 = i__;
	    if ((r__1 = d__[i__2].r, dabs(r__1)) + (r__2 = r_imag(&d__[i__]), 
		    dabs(r__2)) != 0.f) {
		c_div(&q__1, &dl[i__], &d__[i__]);
		fact.r = q__1.r, fact.i = q__1.i;
		i__2 = i__;
		dl[i__2].r = fact.r, dl[i__2].i = fact.i;
		i__2 = i__ + 1;
		i__3 = i__ + 1;
		i__4 = i__;
		q__2.r = fact.r * du[i__4].r - fact.i * du[i__4].i, q__2.i = 
			fact.r * du[i__4].i + fact.i * du[i__4].r;
		q__1.r = d__[i__3].r - q__2.r, q__1.i = d__[i__3].i - q__2.i;
		d__[i__2].r = q__1.r, d__[i__2].i = q__1.i;
	    }
	} else {

/*           Interchange rows I and I+1, eliminate DL(I) */

	    c_div(&q__1, &d__[i__], &dl[i__]);
	    fact.r = q__1.r, fact.i = q__1.i;
	    i__2 = i__;
	    i__3 = i__;
	    d__[i__2].r = dl[i__3].r, d__[i__2].i = dl[i__3].i;
	    i__2 = i__;
	    dl[i__2].r = fact.r, dl[i__2].i = fact.i;
	    i__2 = i__;
	    temp.r = du[i__2].r, temp.i = du[i__2].i;
	    i__2 = i__;
	    i__3 = i__ + 1;
	    du[i__2].r = d__[i__3].r, du[i__2].i = d__[i__3].i;
	    i__2 = i__ + 1;
	    i__3 = i__ + 1;
	    q__2.r = fact.r * d__[i__3].r - fact.i * d__[i__3].i, q__2.i = 
		    fact.r * d__[i__3].i + fact.i * d__[i__3].r;
	    q__1.r = temp.r - q__2.r, q__1.i = temp.i - q__2.i;
	    d__[i__2].r = q__1.r, d__[i__2].i = q__1.i;
	    i__2 = i__;
	    i__3 = i__ + 1;
	    du2[i__2].r = du[i__3].r, du2[i__2].i = du[i__3].i;
	    i__2 = i__ + 1;
	    q__2.r = -fact.r, q__2.i = -fact.i;
	    i__3 = i__ + 1;
	    q__1.r = q__2.r * du[i__3].r - q__2.i * du[i__3].i, q__1.i = 
		    q__2.r * du[i__3].i + q__2.i * du[i__3].r;
	    du[i__2].r = q__1.r, du[i__2].i = q__1.i;
	    ipiv[i__] = i__ + 1;
	}
/* L30: */
    }
    if (*n > 1) {
	i__ = *n - 1;
	i__1 = i__;
	i__2 = i__;
	if ((r__1 = d__[i__1].r, dabs(r__1)) + (r__2 = r_imag(&d__[i__]), 
		dabs(r__2)) >= (r__3 = dl[i__2].r, dabs(r__3)) + (r__4 = 
		r_imag(&dl[i__]), dabs(r__4))) {
	    i__1 = i__;
	    if ((r__1 = d__[i__1].r, dabs(r__1)) + (r__2 = r_imag(&d__[i__]), 
		    dabs(r__2)) != 0.f) {
		c_div(&q__1, &dl[i__], &d__[i__]);
		fact.r = q__1.r, fact.i = q__1.i;
		i__1 = i__;
		dl[i__1].r = fact.r, dl[i__1].i = fact.i;
		i__1 = i__ + 1;
		i__2 = i__ + 1;
		i__3 = i__;
		q__2.r = fact.r * du[i__3].r - fact.i * du[i__3].i, q__2.i = 
			fact.r * du[i__3].i + fact.i * du[i__3].r;
		q__1.r = d__[i__2].r - q__2.r, q__1.i = d__[i__2].i - q__2.i;
		d__[i__1].r = q__1.r, d__[i__1].i = q__1.i;
	    }
	} else {
	    c_div(&q__1, &d__[i__], &dl[i__]);
	    fact.r = q__1.r, fact.i = q__1.i;
	    i__1 = i__;
	    i__2 = i__;
	    d__[i__1].r = dl[i__2].r, d__[i__1].i = dl[i__2].i;
	    i__1 = i__;
	    dl[i__1].r = fact.r, dl[i__1].i = fact.i;
	    i__1 = i__;
	    temp.r = du[i__1].r, temp.i = du[i__1].i;
	    i__1 = i__;
	    i__2 = i__ + 1;
	    du[i__1].r = d__[i__2].r, du[i__1].i = d__[i__2].i;
	    i__1 = i__ + 1;
	    i__2 = i__ + 1;
	    q__2.r = fact.r * d__[i__2].r - fact.i * d__[i__2].i, q__2.i = 
		    fact.r * d__[i__2].i + fact.i * d__[i__2].r;
	    q__1.r = temp.r - q__2.r, q__1.i = temp.i - q__2.i;
	    d__[i__1].r = q__1.r, d__[i__1].i = q__1.i;
	    ipiv[i__] = i__ + 1;
	}
    }

/*     Check for a zero on the diagonal of U. */

    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
	i__2 = i__;
	if ((r__1 = d__[i__2].r, dabs(r__1)) + (r__2 = r_imag(&d__[i__]), 
		dabs(r__2)) == 0.f) {
	    *info = i__;
	    goto L50;
	}
/* L40: */
    }
L50:

    return 0;

/*     End of CGTTRF */

} /* cgttrf_ */

