text: /* stbt02.f -- translated by f2c (version 20061008).
     You must link the resulting object file with libf2c:
  	on Microsoft Windows system, link with libf2c.lib;
  	on Linux or Unix systems, link with .../path/to/libf2c.a -lm
  	or, if you install libf2c.a in a standard place, with -lf2c -lm
  	-- in that order, at the end of the command line, as in
  		cc *.o -lf2c -lm
  	Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,
  
  		http://www.netlib.org/f2c/libf2c.zip
  */
  
  #include "f2c.h"
  #include "blaswrap.h"
  
  /* Table of constant values */
  
  static integer c__1 = 1;
  static real c_b10 = -1.f;
  
  /* Subroutine */ int stbt02_(char *uplo, char *trans, char *diag, integer *n, 
  	integer *kd, integer *nrhs, real *ab, integer *ldab, real *x, integer 
  	*ldx, real *b, integer *ldb, real *work, real *resid)
  {
      /* System generated locals */
      integer ab_dim1, ab_offset, b_dim1, b_offset, x_dim1, x_offset, i__1;
      real r__1, r__2;
  
      /* Local variables */
      integer j;
      real eps;
      extern logical lsame_(char *, char *);
      real anorm, bnorm;
      extern doublereal sasum_(integer *, real *, integer *);
      extern /* Subroutine */ int stbmv_(char *, char *, char *, integer *, 
  	    integer *, real *, integer *, real *, integer *), scopy_(integer *, real *, integer *, real *, integer *);
      real xnorm;
      extern /* Subroutine */ int saxpy_(integer *, real *, real *, integer *, 
  	    real *, integer *);
      extern doublereal slamch_(char *), slantb_(char *, char *, char *, 
  	     integer *, integer *, real *, integer *, real *);
  
  
  /*  -- LAPACK test routine (version 3.1) -- */
  /*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
  /*     November 2006 */
  
  /*     .. Scalar Arguments .. */
  /*     .. */
  /*     .. Array Arguments .. */
  /*     .. */
  
  /*  Purpose */
  /*  ======= */
  
  /*  STBT02 computes the residual for the computed solution to a */
  /*  triangular system of linear equations  A*x = b  or  A' *x = b when */
  /*  A is a triangular band matrix.  Here A' is the transpose of A and */
  /*  x and b are N by NRHS matrices.  The test ratio is the maximum over */
  /*  the number of right hand sides of */
  /*     norm(b - op(A)*x) / ( norm(op(A)) * norm(x) * EPS ), */
  /*  where op(A) denotes A or A' and EPS is the machine epsilon. */
  
  /*  Arguments */
  /*  ========= */
  
  /*  UPLO    (input) CHARACTER*1 */
  /*          Specifies whether the matrix A is upper or lower triangular. */
  /*          = 'U':  Upper triangular */
  /*          = 'L':  Lower triangular */
  
  /*  TRANS   (input) CHARACTER*1 */
  /*          Specifies the operation applied to A. */
  /*          = 'N':  A *x = b  (No transpose) */
  /*          = 'T':  A'*x = b  (Transpose) */
  /*          = 'C':  A'*x = b  (Conjugate transpose = Transpose) */
  
  /*  DIAG    (input) CHARACTER*1 */
  /*          Specifies whether or not the matrix A is unit triangular. */
  /*          = 'N':  Non-unit triangular */
  /*          = 'U':  Unit triangular */
  
  /*  N       (input) INTEGER */
  /*          The order of the matrix A.  N >= 0. */
  
  /*  KD      (input) INTEGER */
  /*          The number of superdiagonals or subdiagonals of the */
  /*          triangular band matrix A.  KD >= 0. */
  
  /*  NRHS    (input) INTEGER */
  /*          The number of right hand sides, i.e., the number of columns */
  /*          of the matrices X and B.  NRHS >= 0. */
  
  /*  AB      (input) REAL array, dimension (LDAB,N) */
  /*          The upper or lower triangular band matrix A, stored in the */
  /*          first kd+1 rows of the array. The j-th column of A is stored */
  /*          in the j-th column of the array AB as follows: */
  /*          if UPLO = 'U', AB(kd+1+i-j,j) = A(i,j) for max(1,j-kd)<=i<=j; */
  /*          if UPLO = 'L', AB(1+i-j,j)    = A(i,j) for j<=i<=min(n,j+kd). */
  
  /*  LDAB    (input) INTEGER */
  /*          The leading dimension of the array AB.  LDAB >= KD+1. */
  
  /*  X       (input) REAL array, dimension (LDX,NRHS) */
  /*          The computed solution vectors for the system of linear */
  /*          equations. */
  
  /*  LDX     (input) INTEGER */
  /*          The leading dimension of the array X.  LDX >= max(1,N). */
  
  /*  B       (input) REAL array, dimension (LDB,NRHS) */
  /*          The right hand side vectors for the system of linear */
  /*          equations. */
  
  /*  LDB     (input) INTEGER */
  /*          The leading dimension of the array B.  LDB >= max(1,N). */
  
  /*  WORK    (workspace) REAL array, dimension (N) */
  
  /*  RESID   (output) REAL */
  /*          The maximum over the number of right hand sides of */
  /*          norm(op(A)*x - b) / ( norm(op(A)) * norm(x) * EPS ). */
  
  /*  ===================================================================== */
  
  /*     .. Parameters .. */
  /*     .. */
  /*     .. Local Scalars .. */
  /*     .. */
  /*     .. External Functions .. */
  /*     .. */
  /*     .. External Subroutines .. */
  /*     .. */
  /*     .. Intrinsic Functions .. */
  /*     .. */
  /*     .. Executable Statements .. */
  
  /*     Quick exit if N = 0 or NRHS = 0 */
  
      /* Parameter adjustments */
      ab_dim1 = *ldab;
      ab_offset = 1 + ab_dim1;
      ab -= ab_offset;
      x_dim1 = *ldx;
      x_offset = 1 + x_dim1;
      x -= x_offset;
      b_dim1 = *ldb;
      b_offset = 1 + b_dim1;
      b -= b_offset;
      --work;
  
      /* Function Body */
      if (*n <= 0 || *nrhs <= 0) {
  	*resid = 0.f;
  	return 0;
      }
  
  /*     Compute the 1-norm of A or A'. */
  
      if (lsame_(trans, "N")) {
  	anorm = slantb_("1", uplo, diag, n, kd, &ab[ab_offset], ldab, &work[1]
  );
      } else {
  	anorm = slantb_("I", uplo, diag, n, kd, &ab[ab_offset], ldab, &work[1]
  );
      }
  
  /*     Exit with RESID = 1/EPS if ANORM = 0. */
  
      eps = slamch_("Epsilon");
      if (anorm <= 0.f) {
  	*resid = 1.f / eps;
  	return 0;
      }
  
  /*     Compute the maximum over the number of right hand sides of */
  /*        norm(op(A)*x - b) / ( norm(op(A)) * norm(x) * EPS ). */
  
      *resid = 0.f;
      i__1 = *nrhs;
      for (j = 1; j <= i__1; ++j) {
  	scopy_(n, &x[j * x_dim1 + 1], &c__1, &work[1], &c__1);
  	stbmv_(uplo, trans, diag, n, kd, &ab[ab_offset], ldab, &work[1], &
  		c__1);
  	saxpy_(n, &c_b10, &b[j * b_dim1 + 1], &c__1, &work[1], &c__1);
  	bnorm = sasum_(n, &work[1], &c__1);
  	xnorm = sasum_(n, &x[j * x_dim1 + 1], &c__1);
  	if (xnorm <= 0.f) {
  	    *resid = 1.f / eps;
  	} else {
  /* Computing MAX */
  	    r__1 = *resid, r__2 = bnorm / anorm / xnorm / eps;
  	    *resid = dmax(r__1,r__2);
  	}
  /* L10: */
      }
  
      return 0;
  
  /*     End of STBT02 */
  
  } /* stbt02_ */
  