 LAPACK 3.11.0 LAPACK: Linear Algebra PACKage
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## ◆ cpot02()

 subroutine cpot02 ( character UPLO, integer N, integer NRHS, complex, dimension( lda, * ) A, integer LDA, complex, dimension( ldx, * ) X, integer LDX, complex, dimension( ldb, * ) B, integer LDB, real, dimension( * ) RWORK, real RESID )

CPOT02

Purpose:
``` CPOT02 computes the residual for the solution of a Hermitian system
of linear equations  A*x = b:

RESID = norm(B - A*X) / ( norm(A) * norm(X) * EPS ),

where EPS is the machine epsilon.```
Parameters
 [in] UPLO ``` UPLO is CHARACTER*1 Specifies whether the upper or lower triangular part of the Hermitian matrix A is stored: = 'U': Upper triangular = 'L': Lower triangular``` [in] N ``` N is INTEGER The number of rows and columns of the matrix A. N >= 0.``` [in] NRHS ``` NRHS is INTEGER The number of columns of B, the matrix of right hand sides. NRHS >= 0.``` [in] A ``` A is COMPLEX array, dimension (LDA,N) The original Hermitian matrix A.``` [in] LDA ``` LDA is INTEGER The leading dimension of the array A. LDA >= max(1,N)``` [in] X ``` X is COMPLEX array, dimension (LDX,NRHS) The computed solution vectors for the system of linear equations.``` [in] LDX ``` LDX is INTEGER The leading dimension of the array X. LDX >= max(1,N).``` [in,out] B ``` B is COMPLEX array, dimension (LDB,NRHS) On entry, the right hand side vectors for the system of linear equations. On exit, B is overwritten with the difference B - A*X.``` [in] LDB ``` LDB is INTEGER The leading dimension of the array B. LDB >= max(1,N).``` [out] RWORK ` RWORK is REAL array, dimension (N)` [out] RESID ``` RESID is REAL The maximum over the number of right hand sides of norm(B - A*X) / ( norm(A) * norm(X) * EPS ).```

Definition at line 125 of file cpot02.f.

127*
128* -- LAPACK test routine --
129* -- LAPACK is a software package provided by Univ. of Tennessee, --
130* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
131*
132* .. Scalar Arguments ..
133 CHARACTER UPLO
134 INTEGER LDA, LDB, LDX, N, NRHS
135 REAL RESID
136* ..
137* .. Array Arguments ..
138 REAL RWORK( * )
139 COMPLEX A( LDA, * ), B( LDB, * ), X( LDX, * )
140* ..
141*
142* =====================================================================
143*
144* .. Parameters ..
145 REAL ZERO, ONE
146 parameter( zero = 0.0e+0, one = 1.0e+0 )
147 COMPLEX CONE
148 parameter( cone = ( 1.0e+0, 0.0e+0 ) )
149* ..
150* .. Local Scalars ..
151 INTEGER J
152 REAL ANORM, BNORM, EPS, XNORM
153* ..
154* .. External Functions ..
155 REAL CLANHE, SCASUM, SLAMCH
156 EXTERNAL clanhe, scasum, slamch
157* ..
158* .. External Subroutines ..
159 EXTERNAL chemm
160* ..
161* .. Intrinsic Functions ..
162 INTRINSIC max
163* ..
164* .. Executable Statements ..
165*
166* Quick exit if N = 0 or NRHS = 0.
167*
168 IF( n.LE.0 .OR. nrhs.LE.0 ) THEN
169 resid = zero
170 RETURN
171 END IF
172*
173* Exit with RESID = 1/EPS if ANORM = 0.
174*
175 eps = slamch( 'Epsilon' )
176 anorm = clanhe( '1', uplo, n, a, lda, rwork )
177 IF( anorm.LE.zero ) THEN
178 resid = one / eps
179 RETURN
180 END IF
181*
182* Compute B - A*X
183*
184 CALL chemm( 'Left', uplo, n, nrhs, -cone, a, lda, x, ldx, cone, b,
185 \$ ldb )
186*
187* Compute the maximum over the number of right hand sides of
188* norm( B - A*X ) / ( norm(A) * norm(X) * EPS ) .
189*
190 resid = zero
191 DO 10 j = 1, nrhs
192 bnorm = scasum( n, b( 1, j ), 1 )
193 xnorm = scasum( n, x( 1, j ), 1 )
194 IF( xnorm.LE.zero ) THEN
195 resid = one / eps
196 ELSE
197 resid = max( resid, ( ( bnorm/anorm )/xnorm )/eps )
198 END IF
199 10 CONTINUE
200*
201 RETURN
202*
203* End of CPOT02
204*
subroutine chemm(SIDE, UPLO, M, N, ALPHA, A, LDA, B, LDB, BETA, C, LDC)
CHEMM
Definition: chemm.f:191
real function clanhe(NORM, UPLO, N, A, LDA, WORK)
CLANHE returns the value of the 1-norm, or the Frobenius norm, or the infinity norm,...
Definition: clanhe.f:124
real function scasum(N, CX, INCX)
SCASUM
Definition: scasum.f:72
real function slamch(CMACH)
SLAMCH
Definition: slamch.f:68
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