LAPACK  3.6.1
LAPACK: Linear Algebra PACKage
subroutine dtpt06 ( double precision  RCOND,
double precision  RCONDC,
character  UPLO,
character  DIAG,
integer  N,
double precision, dimension( * )  AP,
double precision, dimension( * )  WORK,
double precision  RAT 
)

DTPT06

Purpose: 
 DTPT06 computes a test ratio comparing RCOND (the reciprocal
 condition number of a triangular matrix A) and RCONDC, the estimate
 computed by DTPCON.  Information about the triangular matrix A is
 used if one estimate is zero and the other is non-zero to decide if
 underflow in the estimate is justified.
Parameters
[in]RCOND
          RCOND is DOUBLE PRECISION
          The estimate of the reciprocal condition number obtained by
          forming the explicit inverse of the matrix A and computing
          RCOND = 1/( norm(A) * norm(inv(A)) ).
[in]RCONDC
          RCONDC is DOUBLE PRECISION
          The estimate of the reciprocal condition number computed by
          DTPCON.
[in]UPLO
          UPLO is CHARACTER
          Specifies whether the matrix A is upper or lower triangular.
          = 'U':  Upper triangular
          = 'L':  Lower triangular
[in]DIAG
          DIAG is CHARACTER
          Specifies whether or not the matrix A is unit triangular.
          = 'N':  Non-unit triangular
          = 'U':  Unit triangular
[in]N
          N is INTEGER
          The order of the matrix A.  N >= 0.
[in]AP
          AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
          The upper or lower triangular matrix A, packed columnwise in
          a linear array.  The j-th column of A is stored in the array
          AP as follows:
          if UPLO = 'U', AP((j-1)*j/2 + i) = A(i,j) for 1<=i<=j;
          if UPLO = 'L',
             AP((j-1)*(n-j) + j*(j+1)/2 + i-j) = A(i,j) for j<=i<=n.
[out]WORK
          WORK is DOUBLE PRECISION array, dimension (N)
[out]RAT
          RAT is DOUBLE PRECISION
          The test ratio.  If both RCOND and RCONDC are nonzero,
             RAT = MAX( RCOND, RCONDC )/MIN( RCOND, RCONDC ) - 1.
          If RAT = 0, the two estimates are exactly the same.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
November 2011

Definition at line 113 of file dtpt06.f.

113 *
114 * -- LAPACK test routine (version 3.4.0) --
115 * -- LAPACK is a software package provided by Univ. of Tennessee, --
116 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
117 * November 2011
118 *
119 * .. Scalar Arguments ..
120  CHARACTER diag, uplo
121  INTEGER n
122  DOUBLE PRECISION rat, rcond, rcondc
123 * ..
124 * .. Array Arguments ..
125  DOUBLE PRECISION ap( * ), work( * )
126 * ..
127 *
128 * =====================================================================
129 *
130 * .. Parameters ..
131  DOUBLE PRECISION zero, one
132  parameter ( zero = 0.0d+0, one = 1.0d+0 )
133 * ..
134 * .. Local Scalars ..
135  DOUBLE PRECISION anorm, bignum, eps, rmax, rmin, smlnum
136 * ..
137 * .. External Functions ..
138  DOUBLE PRECISION dlamch, dlantp
139  EXTERNAL dlamch, dlantp
140 * ..
141 * .. Intrinsic Functions ..
142  INTRINSIC max, min
143 * ..
144 * .. External Subroutines ..
145  EXTERNAL dlabad
146 * ..
147 * .. Executable Statements ..
148 *
149  eps = dlamch( 'Epsilon' )
150  rmax = max( rcond, rcondc )
151  rmin = min( rcond, rcondc )
152 *
153 * Do the easy cases first.
154 *
155  IF( rmin.LT.zero ) THEN
156 *
157 * Invalid value for RCOND or RCONDC, return 1/EPS.
158 *
159  rat = one / eps
160 *
161  ELSE IF( rmin.GT.zero ) THEN
162 *
163 * Both estimates are positive, return RMAX/RMIN - 1.
164 *
165  rat = rmax / rmin - one
166 *
167  ELSE IF( rmax.EQ.zero ) THEN
168 *
169 * Both estimates zero.
170 *
171  rat = zero
172 *
173  ELSE
174 *
175 * One estimate is zero, the other is non-zero. If the matrix is
176 * ill-conditioned, return the nonzero estimate multiplied by
177 * 1/EPS; if the matrix is badly scaled, return the nonzero
178 * estimate multiplied by BIGNUM/TMAX, where TMAX is the maximum
179 * element in absolute value in A.
180 *
181  smlnum = dlamch( 'Safe minimum' )
182  bignum = one / smlnum
183  CALL dlabad( smlnum, bignum )
184  anorm = dlantp( 'M', uplo, diag, n, ap, work )
185 *
186  rat = rmax*( min( bignum / max( one, anorm ), one / eps ) )
187  END IF
188 *
189  RETURN
190 *
191 * End of DTPT06
192 *
dlamch
double precision function dlamch(CMACH)
DLAMCH
Definition: dlamch.f:65
dlantp
double precision function dlantp(NORM, UPLO, DIAG, N, AP, WORK)
DLANTP returns the value of the 1-norm, or the Frobenius norm, or the infinity norm, or the element of largest absolute value of a triangular matrix supplied in packed form.
Definition: dlantp.f:126
dlabad
subroutine dlabad(SMALL, LARGE)
DLABAD
Definition: dlabad.f:76

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