 LAPACK  3.10.0 LAPACK: Linear Algebra PACKage

## ◆ ctpt02()

 subroutine ctpt02 ( character UPLO, character TRANS, character DIAG, integer N, integer NRHS, complex, dimension( * ) AP, complex, dimension( ldx, * ) X, integer LDX, complex, dimension( ldb, * ) B, integer LDB, complex, dimension( * ) WORK, real, dimension( * ) RWORK, real RESID )

CTPT02

Purpose:
``` CTPT02 computes the residual for the computed solution to a
triangular system of linear equations  A*x = b,  A**T *x = b,  or
A**H *x = b, when the triangular matrix A is stored in packed format.
Here A**T denotes the transpose of A, A**H denotes the conjugate
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
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, A**T, or A**H, and EPS is the machine epsilon.```
Parameters
 [in] UPLO ``` UPLO is CHARACTER*1 Specifies whether the matrix A is upper or lower triangular. = 'U': Upper triangular = 'L': Lower triangular``` [in] TRANS ``` TRANS is CHARACTER*1 Specifies the operation applied to A. = 'N': A *x = b (No transpose) = 'T': A**T *x = b (Transpose) = 'C': A**H *x = b (Conjugate transpose)``` [in] DIAG ``` DIAG is CHARACTER*1 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] NRHS ``` NRHS is INTEGER The number of right hand sides, i.e., the number of columns of the matrices X and B. NRHS >= 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.``` [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] B ``` B is COMPLEX array, dimension (LDB,NRHS) The right hand side vectors for the system of linear equations.``` [in] LDB ``` LDB is INTEGER The leading dimension of the array B. LDB >= max(1,N).``` [out] WORK ` WORK is COMPLEX array, dimension (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(op(A)*x - b) / ( norm(op(A)) * norm(x) * EPS ).```

Definition at line 147 of file ctpt02.f.

149 *
150 * -- LAPACK test routine --
151 * -- LAPACK is a software package provided by Univ. of Tennessee, --
152 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
153 *
154 * .. Scalar Arguments ..
155  CHARACTER DIAG, TRANS, UPLO
156  INTEGER LDB, LDX, N, NRHS
157  REAL RESID
158 * ..
159 * .. Array Arguments ..
160  REAL RWORK( * )
161  COMPLEX AP( * ), B( LDB, * ), WORK( * ), X( LDX, * )
162 * ..
163 *
164 * =====================================================================
165 *
166 * .. Parameters ..
167  REAL ZERO, ONE
168  parameter( zero = 0.0e+0, one = 1.0e+0 )
169 * ..
170 * .. Local Scalars ..
171  INTEGER J
172  REAL ANORM, BNORM, EPS, XNORM
173 * ..
174 * .. External Functions ..
175  LOGICAL LSAME
176  REAL CLANTP, SCASUM, SLAMCH
177  EXTERNAL lsame, clantp, scasum, slamch
178 * ..
179 * .. External Subroutines ..
180  EXTERNAL caxpy, ccopy, ctpmv
181 * ..
182 * .. Intrinsic Functions ..
183  INTRINSIC cmplx, max
184 * ..
185 * .. Executable Statements ..
186 *
187 * Quick exit if N = 0 or NRHS = 0
188 *
189  IF( n.LE.0 .OR. nrhs.LE.0 ) THEN
190  resid = zero
191  RETURN
192  END IF
193 *
194 * Compute the 1-norm of A or A**H.
195 *
196  IF( lsame( trans, 'N' ) ) THEN
197  anorm = clantp( '1', uplo, diag, n, ap, rwork )
198  ELSE
199  anorm = clantp( 'I', uplo, diag, n, ap, rwork )
200  END IF
201 *
202 * Exit with RESID = 1/EPS if ANORM = 0.
203 *
204  eps = slamch( 'Epsilon' )
205  IF( anorm.LE.zero ) THEN
206  resid = one / eps
207  RETURN
208  END IF
209 *
210 * Compute the maximum over the number of right hand sides of
211 * norm(op(A)*x - b) / ( norm(op(A)) * norm(x) * EPS ).
212 *
213  resid = zero
214  DO 10 j = 1, nrhs
215  CALL ccopy( n, x( 1, j ), 1, work, 1 )
216  CALL ctpmv( uplo, trans, diag, n, ap, work, 1 )
217  CALL caxpy( n, cmplx( -one ), b( 1, j ), 1, work, 1 )
218  bnorm = scasum( n, work, 1 )
219  xnorm = scasum( n, x( 1, j ), 1 )
220  IF( xnorm.LE.zero ) THEN
221  resid = one / eps
222  ELSE
223  resid = max( resid, ( ( bnorm / anorm ) / xnorm ) / eps )
224  END IF
225  10 CONTINUE
226 *
227  RETURN
228 *
229 * End of CTPT02
230 *
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine ccopy(N, CX, INCX, CY, INCY)
CCOPY
Definition: ccopy.f:81
subroutine caxpy(N, CA, CX, INCX, CY, INCY)
CAXPY
Definition: caxpy.f:88
subroutine ctpmv(UPLO, TRANS, DIAG, N, AP, X, INCX)
CTPMV
Definition: ctpmv.f:142
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 scasum(N, CX, INCX)
SCASUM
Definition: scasum.f:72
real function slamch(CMACH)
SLAMCH
Definition: slamch.f:68
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