LAPACK  3.10.1 LAPACK: Linear Algebra PACKage

◆ ctpt03()

 subroutine ctpt03 ( character UPLO, character TRANS, character DIAG, integer N, integer NRHS, complex, dimension( * ) AP, real SCALE, real, dimension( * ) CNORM, real TSCAL, complex, dimension( ldx, * ) X, integer LDX, complex, dimension( ldb, * ) B, integer LDB, complex, dimension( * ) WORK, real RESID )

CTPT03

Purpose:
``` CTPT03 computes the residual for the solution to a scaled triangular
system of equations A*x = s*b,  A**T *x = s*b,  or  A**H *x = s*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, s is a scalar, and x and b are N by NRHS matrices.  The test ratio
is the maximum over the number of right hand sides of
norm(s*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 = s*b (No transpose) = 'T': A**T *x = s*b (Transpose) = 'C': A**H *x = s*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] SCALE ``` SCALE is REAL The scaling factor s used in solving the triangular system.``` [in] CNORM ``` CNORM is REAL array, dimension (N) The 1-norms of the columns of A, not counting the diagonal.``` [in] TSCAL ``` TSCAL is REAL The scaling factor used in computing the 1-norms in CNORM. CNORM actually contains the column norms of TSCAL*A.``` [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] RESID ``` RESID is REAL The maximum over the number of right hand sides of norm(op(A)*x - s*b) / ( norm(op(A)) * norm(x) * EPS ).```

Definition at line 160 of file ctpt03.f.

162 *
163 * -- LAPACK test routine --
164 * -- LAPACK is a software package provided by Univ. of Tennessee, --
165 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
166 *
167 * .. Scalar Arguments ..
168  CHARACTER DIAG, TRANS, UPLO
169  INTEGER LDB, LDX, N, NRHS
170  REAL RESID, SCALE, TSCAL
171 * ..
172 * .. Array Arguments ..
173  REAL CNORM( * )
174  COMPLEX AP( * ), B( LDB, * ), WORK( * ), X( LDX, * )
175 * ..
176 *
177 * =====================================================================
178 *
179 * .. Parameters ..
180  REAL ONE, ZERO
181  parameter( one = 1.0e+0, zero = 0.0e+0 )
182 * ..
183 * .. Local Scalars ..
184  INTEGER IX, J, JJ
185  REAL EPS, ERR, SMLNUM, TNORM, XNORM, XSCAL
186 * ..
187 * .. External Functions ..
188  LOGICAL LSAME
189  INTEGER ICAMAX
190  REAL SLAMCH
191  EXTERNAL lsame, icamax, slamch
192 * ..
193 * .. External Subroutines ..
194  EXTERNAL caxpy, ccopy, csscal, ctpmv
195 * ..
196 * .. Intrinsic Functions ..
197  INTRINSIC abs, cmplx, max, real
198 * ..
199 * .. Executable Statements ..
200 *
201 * Quick exit if N = 0.
202 *
203  IF( n.LE.0 .OR. nrhs.LE.0 ) THEN
204  resid = zero
205  RETURN
206  END IF
207  eps = slamch( 'Epsilon' )
208  smlnum = slamch( 'Safe minimum' )
209 *
210 * Compute the norm of the triangular matrix A using the column
211 * norms already computed by CLATPS.
212 *
213  tnorm = 0.
214  IF( lsame( diag, 'N' ) ) THEN
215  IF( lsame( uplo, 'U' ) ) THEN
216  jj = 1
217  DO 10 j = 1, n
218  tnorm = max( tnorm, tscal*abs( ap( jj ) )+cnorm( j ) )
219  jj = jj + j + 1
220  10 CONTINUE
221  ELSE
222  jj = 1
223  DO 20 j = 1, n
224  tnorm = max( tnorm, tscal*abs( ap( jj ) )+cnorm( j ) )
225  jj = jj + n - j + 1
226  20 CONTINUE
227  END IF
228  ELSE
229  DO 30 j = 1, n
230  tnorm = max( tnorm, tscal+cnorm( j ) )
231  30 CONTINUE
232  END IF
233 *
234 * Compute the maximum over the number of right hand sides of
235 * norm(op(A)*x - s*b) / ( norm(A) * norm(x) * EPS ).
236 *
237  resid = zero
238  DO 40 j = 1, nrhs
239  CALL ccopy( n, x( 1, j ), 1, work, 1 )
240  ix = icamax( n, work, 1 )
241  xnorm = max( one, abs( x( ix, j ) ) )
242  xscal = ( one / xnorm ) / real( n )
243  CALL csscal( n, xscal, work, 1 )
244  CALL ctpmv( uplo, trans, diag, n, ap, work, 1 )
245  CALL caxpy( n, cmplx( -scale*xscal ), b( 1, j ), 1, work, 1 )
246  ix = icamax( n, work, 1 )
247  err = tscal*abs( work( ix ) )
248  ix = icamax( n, x( 1, j ), 1 )
249  xnorm = abs( x( ix, j ) )
250  IF( err*smlnum.LE.xnorm ) THEN
251  IF( xnorm.GT.zero )
252  \$ err = err / xnorm
253  ELSE
254  IF( err.GT.zero )
255  \$ err = one / eps
256  END IF
257  IF( err*smlnum.LE.tnorm ) THEN
258  IF( tnorm.GT.zero )
259  \$ err = err / tnorm
260  ELSE
261  IF( err.GT.zero )
262  \$ err = one / eps
263  END IF
264  resid = max( resid, err )
265  40 CONTINUE
266 *
267  RETURN
268 *
269 * End of CTPT03
270 *
integer function icamax(N, CX, INCX)
ICAMAX
Definition: icamax.f:71
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine ccopy(N, CX, INCX, CY, INCY)
CCOPY
Definition: ccopy.f:81
subroutine csscal(N, SA, CX, INCX)
CSSCAL
Definition: csscal.f:78
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 slamch(CMACH)
SLAMCH
Definition: slamch.f:68
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