LAPACK  3.6.1 LAPACK: Linear Algebra PACKage
 integer function ilaenv ( integer ISPEC, character*( * ) NAME, character*( * ) OPTS, integer N1, integer N2, integer N3, integer N4 )

ILAENV

Purpose:
``` ILAENV returns problem-dependent parameters for the local
environment.  See ISPEC for a description of the parameters.

In this version, the problem-dependent parameters are contained in
the integer array IPARMS in the common block CLAENV and the value
with index ISPEC is copied to ILAENV.  This version of ILAENV is
to be used in conjunction with XLAENV in TESTING and TIMING.```
Parameters
 [in] ISPEC ``` ISPEC is INTEGER Specifies the parameter to be returned as the value of ILAENV. = 1: the optimal blocksize; if this value is 1, an unblocked algorithm will give the best performance. = 2: the minimum block size for which the block routine should be used; if the usable block size is less than this value, an unblocked routine should be used. = 3: the crossover point (in a block routine, for N less than this value, an unblocked routine should be used) = 4: the number of shifts, used in the nonsymmetric eigenvalue routines = 5: the minimum column dimension for blocking to be used; rectangular blocks must have dimension at least k by m, where k is given by ILAENV(2,...) and m by ILAENV(5,...) = 6: the crossover point for the SVD (when reducing an m by n matrix to bidiagonal form, if max(m,n)/min(m,n) exceeds this value, a QR factorization is used first to reduce the matrix to a triangular form.) = 7: the number of processors = 8: the crossover point for the multishift QR and QZ methods for nonsymmetric eigenvalue problems. = 9: maximum size of the subproblems at the bottom of the computation tree in the divide-and-conquer algorithm =10: ieee NaN arithmetic can be trusted not to trap =11: infinity arithmetic can be trusted not to trap Other specifications (up to 100) can be added later.``` [in] NAME ``` NAME is CHARACTER*(*) The name of the calling subroutine.``` [in] OPTS ``` OPTS is CHARACTER*(*) The character options to the subroutine NAME, concatenated into a single character string. For example, UPLO = 'U', TRANS = 'T', and DIAG = 'N' for a triangular routine would be specified as OPTS = 'UTN'.``` [in] N1 ` N1 is INTEGER` [in] N2 ` N2 is INTEGER` [in] N3 ` N3 is INTEGER` [in] N4 ``` N4 is INTEGER Problem dimensions for the subroutine NAME; these may not all be required.```
Returns
ILAENV
```          ILAENV is INTEGER
>= 0: the value of the parameter specified by ISPEC
< 0:  if ILAENV = -k, the k-th argument had an illegal value.```
Date
November 2011
Further Details:
```  The following conventions have been used when calling ILAENV from the
LAPACK routines:
1)  OPTS is a concatenation of all of the character options to
subroutine NAME, in the same order that they appear in the
argument list for NAME, even if they are not used in determining
the value of the parameter specified by ISPEC.
2)  The problem dimensions N1, N2, N3, N4 are specified in the order
that they appear in the argument list for NAME.  N1 is used
first, N2 second, and so on, and unused problem dimensions are
passed a value of -1.
3)  The parameter value returned by ILAENV is checked for validity in
the calling subroutine.  For example, ILAENV is used to retrieve
the optimal blocksize for STRTRI as follows:

NB = ILAENV( 1, 'STRTRI', UPLO // DIAG, N, -1, -1, -1 )
IF( NB.LE.1 ) NB = MAX( 1, N )```

Definition at line 152 of file ilaenv.f.

152 *
153 * -- LAPACK test routine (version 3.4.0) --
154 * -- LAPACK is a software package provided by Univ. of Tennessee, --
155 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
156 * November 2011
157 *
158 * .. Scalar Arguments ..
159  CHARACTER*( * ) name, opts
160  INTEGER ispec, n1, n2, n3, n4
161 * ..
162 *
163 * =====================================================================
164 *
165 * .. Intrinsic Functions ..
166  INTRINSIC int, min, real
167 * ..
168 * .. External Functions ..
169  INTEGER ieeeck
170  EXTERNAL ieeeck
171 * ..
172 * .. Arrays in Common ..
173  INTEGER iparms( 100 )
174 * ..
175 * .. Common blocks ..
176  COMMON / claenv / iparms
177 * ..
178 * .. Save statement ..
179  SAVE / claenv /
180 * ..
181 * .. Executable Statements ..
182 *
183  IF( ispec.GE.1 .AND. ispec.LE.5 ) THEN
184 *
185 * Return a value from the common block.
186 *
187  ilaenv = iparms( ispec )
188 *
189  ELSE IF( ispec.EQ.6 ) THEN
190 *
191 * Compute SVD crossover point.
192 *
193  ilaenv = int( REAL( MIN( N1, N2 ) )*1.6e0 )
194 *
195  ELSE IF( ispec.GE.7 .AND. ispec.LE.9 ) THEN
196 *
197 * Return a value from the common block.
198 *
199  ilaenv = iparms( ispec )
200 *
201  ELSE IF( ispec.EQ.10 ) THEN
202 *
203 * IEEE NaN arithmetic can be trusted not to trap
204 *
205 C ILAENV = 0
206  ilaenv = 1
207  IF( ilaenv.EQ.1 ) THEN
208  ilaenv = ieeeck( 1, 0.0, 1.0 )
209  END IF
210 *
211  ELSE IF( ispec.EQ.11 ) THEN
212 *
213 * Infinity arithmetic can be trusted not to trap
214 *
215 C ILAENV = 0
216  ilaenv = 1
217  IF( ilaenv.EQ.1 ) THEN
218  ilaenv = ieeeck( 0, 0.0, 1.0 )
219  END IF
220 *
221  ELSE
222 *
223 * Invalid value for ISPEC
224 *
225  ilaenv = -1
226  END IF
227 *
228  RETURN
229 *
230 * End of ILAENV
231 *
integer function ieeeck(ISPEC, ZERO, ONE)
Definition: tstiee.f:626
integer function ilaenv(ISPEC, NAME, OPTS, N1, N2, N3, N4)
Definition: tstiee.f:83

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