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

/* Subroutine */ int cpttrf_(integer *n, real *d__, complex *e, 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   
    =======   

    CPTTRF computes the L*D*L' factorization of a complex Hermitian   
    positive definite tridiagonal matrix A.  The factorization may also   
    be regarded as having the form A = U'*D*U.   

    Arguments   
    =========   

    N       (input) INTEGER   
            The order of the matrix A.  N >= 0.   

    D       (input/output) REAL array, dimension (N)   
            On entry, the n diagonal elements of the tridiagonal matrix   
            A.  On exit, the n diagonal elements of the diagonal matrix   
            D from the L*D*L' factorization of A.   

    E       (input/output) COMPLEX array, dimension (N-1)   
            On entry, the (n-1) subdiagonal elements of the tridiagonal   
            matrix A.  On exit, the (n-1) subdiagonal elements of the   
            unit bidiagonal factor L from the L*D*L' factorization of A.   
            E can also be regarded as the superdiagonal of the unit   
            bidiagonal factor U from the U'*D*U factorization of A.   

    INFO    (output) INTEGER   
            = 0: successful exit   
            < 0: if INFO = -k, the k-th argument had an illegal value   
            > 0: if INFO = k, the leading minor of order k is not   
                 positive definite; if k < N, the factorization could not   
                 be completed, while if k = N, the factorization was   
                 completed, but D(N) = 0.   

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


       Test the input parameters.   

       Parameter adjustments */
    /* System generated locals */
    integer i__1, i__2;
    complex q__1;
    /* Builtin functions */
    double r_imag(complex *);
    /* Local variables */
    static real f, g;
    static integer i__, i4;
    extern /* Subroutine */ int xerbla_(char *, integer *);
    static real eii, eir;

    --e;
    --d__;

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

/*     Quick return if possible */

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

/*     Compute the L*D*L' (or U'*D*U) factorization of A. */

    i4 = (*n - 1) % 4;
    i__1 = i4;
    for (i__ = 1; i__ <= i__1; ++i__) {
	if (d__[i__] <= 0.f) {
	    *info = i__;
	    goto L20;
	}
	i__2 = i__;
	eir = e[i__2].r;
	eii = r_imag(&e[i__]);
	f = eir / d__[i__];
	g = eii / d__[i__];
	i__2 = i__;
	q__1.r = f, q__1.i = g;
	e[i__2].r = q__1.r, e[i__2].i = q__1.i;
	d__[i__ + 1] = d__[i__ + 1] - f * eir - g * eii;
/* L10: */
    }

    i__1 = *n - 4;
    for (i__ = i4 + 1; i__ <= i__1; i__ += 4) {

/*        Drop out of the loop if d(i) <= 0: the matrix is not positive   
          definite. */

	if (d__[i__] <= 0.f) {
	    *info = i__;
	    goto L20;
	}

/*        Solve for e(i) and d(i+1). */

	i__2 = i__;
	eir = e[i__2].r;
	eii = r_imag(&e[i__]);
	f = eir / d__[i__];
	g = eii / d__[i__];
	i__2 = i__;
	q__1.r = f, q__1.i = g;
	e[i__2].r = q__1.r, e[i__2].i = q__1.i;
	d__[i__ + 1] = d__[i__ + 1] - f * eir - g * eii;

	if (d__[i__ + 1] <= 0.f) {
	    *info = i__ + 1;
	    goto L20;
	}

/*        Solve for e(i+1) and d(i+2). */

	i__2 = i__ + 1;
	eir = e[i__2].r;
	eii = r_imag(&e[i__ + 1]);
	f = eir / d__[i__ + 1];
	g = eii / d__[i__ + 1];
	i__2 = i__ + 1;
	q__1.r = f, q__1.i = g;
	e[i__2].r = q__1.r, e[i__2].i = q__1.i;
	d__[i__ + 2] = d__[i__ + 2] - f * eir - g * eii;

	if (d__[i__ + 2] <= 0.f) {
	    *info = i__ + 2;
	    goto L20;
	}

/*        Solve for e(i+2) and d(i+3). */

	i__2 = i__ + 2;
	eir = e[i__2].r;
	eii = r_imag(&e[i__ + 2]);
	f = eir / d__[i__ + 2];
	g = eii / d__[i__ + 2];
	i__2 = i__ + 2;
	q__1.r = f, q__1.i = g;
	e[i__2].r = q__1.r, e[i__2].i = q__1.i;
	d__[i__ + 3] = d__[i__ + 3] - f * eir - g * eii;

	if (d__[i__ + 3] <= 0.f) {
	    *info = i__ + 3;
	    goto L20;
	}

/*        Solve for e(i+3) and d(i+4). */

	i__2 = i__ + 3;
	eir = e[i__2].r;
	eii = r_imag(&e[i__ + 3]);
	f = eir / d__[i__ + 3];
	g = eii / d__[i__ + 3];
	i__2 = i__ + 3;
	q__1.r = f, q__1.i = g;
	e[i__2].r = q__1.r, e[i__2].i = q__1.i;
	d__[i__ + 4] = d__[i__ + 4] - f * eir - g * eii;
/* L110: */
    }

/*     Check d(n) for positive definiteness. */

    if (d__[*n] <= 0.f) {
	*info = *n;
    }

L20:
    return 0;

/*     End of CPTTRF */

} /* cpttrf_ */

