text: #include "f2c.h"
  #include "blaswrap.h"
  
  /* Subroutine */ int cptt01_(integer *n, real *d__, complex *e, real *df, 
  	complex *ef, complex *work, real *resid)
  {
      /* System generated locals */
      integer i__1, i__2, i__3, i__4;
      real r__1, r__2;
      complex q__1, q__2, q__3, q__4;
  
      /* Builtin functions */
      void r_cnjg(complex *, complex *);
      double c_abs(complex *);
  
      /* Local variables */
      integer i__;
      complex de;
      real eps, anorm;
      extern doublereal slamch_(char *);
  
  
  /*  -- LAPACK test routine (version 3.1) -- */
  /*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
  /*     November 2006 */
  
  /*     .. Scalar Arguments .. */
  /*     .. */
  /*     .. Array Arguments .. */
  /*     .. */
  
  /*  Purpose */
  /*  ======= */
  
  /*  CPTT01 reconstructs a tridiagonal matrix A from its L*D*L' */
  /*  factorization and computes the residual */
  /*     norm(L*D*L' - A) / ( n * norm(A) * EPS ), */
  /*  where EPS is the machine epsilon. */
  
  /*  Arguments */
  /*  ========= */
  
  /*  N       (input) INTEGTER */
  /*          The order of the matrix A. */
  
  /*  D       (input) REAL array, dimension (N) */
  /*          The n diagonal elements of the tridiagonal matrix A. */
  
  /*  E       (input) COMPLEX array, dimension (N-1) */
  /*          The (n-1) subdiagonal elements of the tridiagonal matrix A. */
  
  /*  DF      (input) REAL array, dimension (N) */
  /*          The n diagonal elements of the factor L from the L*D*L' */
  /*          factorization of A. */
  
  /*  EF      (input) COMPLEX array, dimension (N-1) */
  /*          The (n-1) subdiagonal elements of the factor L from the */
  /*          L*D*L' factorization of A. */
  
  /*  WORK    (workspace) COMPLEX array, dimension (2*N) */
  
  /*  RESID   (output) REAL */
  /*          norm(L*D*L' - A) / (n * norm(A) * EPS) */
  
  /*  ===================================================================== */
  
  /*     .. Parameters .. */
  /*     .. */
  /*     .. Local Scalars .. */
  /*     .. */
  /*     .. External Functions .. */
  /*     .. */
  /*     .. Intrinsic Functions .. */
  /*     .. */
  /*     .. Executable Statements .. */
  
  /*     Quick return if possible */
  
      /* Parameter adjustments */
      --work;
      --ef;
      --df;
      --e;
      --d__;
  
      /* Function Body */
      if (*n <= 0) {
  	*resid = 0.f;
  	return 0;
      }
  
      eps = slamch_("Epsilon");
  
  /*     Construct the difference L*D*L' - A. */
  
      r__1 = df[1] - d__[1];
      work[1].r = r__1, work[1].i = 0.f;
      i__1 = *n - 1;
      for (i__ = 1; i__ <= i__1; ++i__) {
  	i__2 = i__;
  	i__3 = i__;
  	q__1.r = df[i__2] * ef[i__3].r, q__1.i = df[i__2] * ef[i__3].i;
  	de.r = q__1.r, de.i = q__1.i;
  	i__2 = *n + i__;
  	i__3 = i__;
  	q__1.r = de.r - e[i__3].r, q__1.i = de.i - e[i__3].i;
  	work[i__2].r = q__1.r, work[i__2].i = q__1.i;
  	i__2 = i__ + 1;
  	r_cnjg(&q__4, &ef[i__]);
  	q__3.r = de.r * q__4.r - de.i * q__4.i, q__3.i = de.r * q__4.i + de.i 
  		* q__4.r;
  	i__3 = i__ + 1;
  	q__2.r = q__3.r + df[i__3], q__2.i = q__3.i;
  	i__4 = i__ + 1;
  	q__1.r = q__2.r - d__[i__4], q__1.i = q__2.i;
  	work[i__2].r = q__1.r, work[i__2].i = q__1.i;
  /* L10: */
      }
  
  /*     Compute the 1-norms of the tridiagonal matrices A and WORK. */
  
      if (*n == 1) {
  	anorm = d__[1];
  	*resid = c_abs(&work[1]);
      } else {
  /* Computing MAX */
  	r__1 = d__[1] + c_abs(&e[1]), r__2 = d__[*n] + c_abs(&e[*n - 1]);
  	anorm = dmax(r__1,r__2);
  /* Computing MAX */
  	r__1 = c_abs(&work[1]) + c_abs(&work[*n + 1]), r__2 = c_abs(&work[*n])
  		 + c_abs(&work[(*n << 1) - 1]);
  	*resid = dmax(r__1,r__2);
  	i__1 = *n - 1;
  	for (i__ = 2; i__ <= i__1; ++i__) {
  /* Computing MAX */
  	    r__1 = anorm, r__2 = d__[i__] + c_abs(&e[i__]) + c_abs(&e[i__ - 1]
  		    );
  	    anorm = dmax(r__1,r__2);
  /* Computing MAX */
  	    r__1 = *resid, r__2 = c_abs(&work[i__]) + c_abs(&work[*n + i__ - 
  		    1]) + c_abs(&work[*n + i__]);
  	    *resid = dmax(r__1,r__2);
  /* L20: */
  	}
      }
  
  /*     Compute norm(L*D*L' - A) / (n * norm(A) * EPS) */
  
      if (anorm <= 0.f) {
  	if (*resid != 0.f) {
  	    *resid = 1.f / eps;
  	}
      } else {
  	*resid = *resid / (real) (*n) / anorm / eps;
      }
  
      return 0;
  
  /*     End of CPTT01 */
  
  } /* cptt01_ */
  