LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
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◆ ctpt06()

subroutine ctpt06 ( real  RCOND,
real  RCONDC,
character  UPLO,
character  DIAG,
integer  N,
complex, dimension( * )  AP,
real, dimension( * )  RWORK,
real  RAT 
)

CTPT06

Purpose:
 CTPT06 computes a test ratio comparing RCOND (the reciprocal
 condition number of the triangular matrix A) and RCONDC, the estimate
 computed by CTPCON.  Information about the triangular matrix 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 REAL
          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 REAL
          The estimate of the reciprocal condition number computed by
          CTPCON.
[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 COMPLEX 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]RWORK
          RWORK is REAL array, dimension (N)
[out]RAT
          RAT is REAL
          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.

Definition at line 111 of file ctpt06.f.

112*
113* -- LAPACK test routine --
114* -- LAPACK is a software package provided by Univ. of Tennessee, --
115* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
116*
117* .. Scalar Arguments ..
118 CHARACTER DIAG, UPLO
119 INTEGER N
120 REAL RAT, RCOND, RCONDC
121* ..
122* .. Array Arguments ..
123 REAL RWORK( * )
124 COMPLEX AP( * )
125* ..
126*
127* =====================================================================
128*
129* .. Parameters ..
130 REAL ZERO, ONE
131 parameter( zero = 0.0e+0, one = 1.0e+0 )
132* ..
133* .. Local Scalars ..
134 REAL ANORM, BIGNUM, EPS, RMAX, RMIN
135* ..
136* .. External Functions ..
137 REAL CLANTP, SLAMCH
138 EXTERNAL clantp, slamch
139* ..
140* .. Intrinsic Functions ..
141 INTRINSIC max, min
142* ..
143* .. Executable Statements ..
144*
145 eps = slamch( 'Epsilon' )
146 rmax = max( rcond, rcondc )
147 rmin = min( rcond, rcondc )
148*
149* Do the easy cases first.
150*
151 IF( rmin.LT.zero ) THEN
152*
153* Invalid value for RCOND or RCONDC, return 1/EPS.
154*
155 rat = one / eps
156*
157 ELSE IF( rmin.GT.zero ) THEN
158*
159* Both estimates are positive, return RMAX/RMIN - 1.
160*
161 rat = rmax / rmin - one
162*
163 ELSE IF( rmax.EQ.zero ) THEN
164*
165* Both estimates zero.
166*
167 rat = zero
168*
169 ELSE
170*
171* One estimate is zero, the other is non-zero. If the matrix is
172* ill-conditioned, return the nonzero estimate multiplied by
173* 1/EPS; if the matrix is badly scaled, return the nonzero
174* estimate multiplied by BIGNUM/TMAX, where TMAX is the maximum
175* element in absolute value in A.
176*
177 bignum = one / slamch( 'Safe minimum' )
178 anorm = clantp( 'M', uplo, diag, n, ap, rwork )
179*
180 rat = rmax*( min( bignum / max( one, anorm ), one / eps ) )
181 END IF
182*
183 RETURN
184*
185* End of CTPT06
186*
real function clantp(NORM, UPLO, DIAG, N, AP, WORK)
CLANTP returns the value of the 1-norm, or the Frobenius norm, or the infinity norm,...
Definition: clantp.f:125
real function slamch(CMACH)
SLAMCH
Definition: slamch.f:68
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