LAPACK 3.11.0 LAPACK: Linear Algebra PACKage
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## ◆ dtrt06()

 subroutine dtrt06 ( double precision RCOND, double precision RCONDC, character UPLO, character DIAG, integer N, double precision, dimension( lda, * ) A, integer LDA, double precision, dimension( * ) WORK, double precision RAT )

DTRT06

Purpose:
``` DTRT06 computes a test ratio comparing RCOND (the reciprocal
condition number of a triangular matrix A) and RCONDC, the estimate
computed by DTRCON.  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 DTRCON.``` [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] A ``` A is DOUBLE PRECISION array, dimension (LDA,N) The triangular matrix A. If UPLO = 'U', the leading n by n upper triangular part of the array A contains the upper triangular matrix, and the strictly lower triangular part of A is not referenced. If UPLO = 'L', the leading n by n lower triangular part of the array A contains the lower triangular matrix, and the strictly upper triangular part of A is not referenced. If DIAG = 'U', the diagonal elements of A are also not referenced and are assumed to be 1.``` [in] LDA ``` LDA is INTEGER The leading dimension of the array A. LDA >= max(1,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.```

Definition at line 119 of file dtrt06.f.

121*
122* -- LAPACK test routine --
123* -- LAPACK is a software package provided by Univ. of Tennessee, --
124* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
125*
126* .. Scalar Arguments ..
127 CHARACTER DIAG, UPLO
128 INTEGER LDA, N
129 DOUBLE PRECISION RAT, RCOND, RCONDC
130* ..
131* .. Array Arguments ..
132 DOUBLE PRECISION A( LDA, * ), WORK( * )
133* ..
134*
135* =====================================================================
136*
137* .. Parameters ..
138 DOUBLE PRECISION ZERO, ONE
139 parameter( zero = 0.0d+0, one = 1.0d+0 )
140* ..
141* .. Local Scalars ..
142 DOUBLE PRECISION ANORM, BIGNUM, EPS, RMAX, RMIN, SMLNUM
143* ..
144* .. External Functions ..
145 DOUBLE PRECISION DLAMCH, DLANTR
146 EXTERNAL dlamch, dlantr
147* ..
148* .. Intrinsic Functions ..
149 INTRINSIC max, min
150* ..
151* .. External Subroutines ..
153* ..
154* .. Executable Statements ..
155*
156 eps = dlamch( 'Epsilon' )
157 rmax = max( rcond, rcondc )
158 rmin = min( rcond, rcondc )
159*
160* Do the easy cases first.
161*
162 IF( rmin.LT.zero ) THEN
163*
164* Invalid value for RCOND or RCONDC, return 1/EPS.
165*
166 rat = one / eps
167*
168 ELSE IF( rmin.GT.zero ) THEN
169*
170* Both estimates are positive, return RMAX/RMIN - 1.
171*
172 rat = rmax / rmin - one
173*
174 ELSE IF( rmax.EQ.zero ) THEN
175*
176* Both estimates zero.
177*
178 rat = zero
179*
180 ELSE
181*
182* One estimate is zero, the other is non-zero. If the matrix is
183* ill-conditioned, return the nonzero estimate multiplied by
184* 1/EPS; if the matrix is badly scaled, return the nonzero
185* estimate multiplied by BIGNUM/TMAX, where TMAX is the maximum
186* element in absolute value in A.
187*
188 smlnum = dlamch( 'Safe minimum' )
189 bignum = one / smlnum
190 CALL dlabad( smlnum, bignum )
191 anorm = dlantr( 'M', uplo, diag, n, n, a, lda, work )
192*
193 rat = rmax*( min( bignum / max( one, anorm ), one / eps ) )
194 END IF
195*
196 RETURN
197*
198* End of DTRT06
199*
double precision function dlamch(CMACH)
DLAMCH
Definition: dlamch.f:69