LAPACK  3.5.0
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ilaenv.f
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1 *> \brief \b ILAENV
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 * Definition:
9 * ===========
10 *
11 * INTEGER FUNCTION ILAENV( ISPEC, NAME, OPTS, N1, N2, N3,
12 * N4 )
13 *
14 * .. Scalar Arguments ..
15 * CHARACTER*( * ) NAME, OPTS
16 * INTEGER ISPEC, N1, N2, N3, N4
17 * ..
18 *
19 *
20 *> \par Purpose:
21 * =============
22 *>
23 *> \verbatim
24 *>
25 *> ILAENV returns problem-dependent parameters for the local
26 *> environment. See ISPEC for a description of the parameters.
27 *>
28 *> In this version, the problem-dependent parameters are contained in
29 *> the integer array IPARMS in the common block CLAENV and the value
30 *> with index ISPEC is copied to ILAENV. This version of ILAENV is
31 *> to be used in conjunction with XLAENV in TESTING and TIMING.
32 *> \endverbatim
33 *
34 * Arguments:
35 * ==========
36 *
37 *> \param[in] ISPEC
38 *> \verbatim
39 *> ISPEC is INTEGER
40 *> Specifies the parameter to be returned as the value of
41 *> ILAENV.
42 *> = 1: the optimal blocksize; if this value is 1, an unblocked
43 *> algorithm will give the best performance.
44 *> = 2: the minimum block size for which the block routine
45 *> should be used; if the usable block size is less than
46 *> this value, an unblocked routine should be used.
47 *> = 3: the crossover point (in a block routine, for N less
48 *> than this value, an unblocked routine should be used)
49 *> = 4: the number of shifts, used in the nonsymmetric
50 *> eigenvalue routines
51 *> = 5: the minimum column dimension for blocking to be used;
52 *> rectangular blocks must have dimension at least k by m,
53 *> where k is given by ILAENV(2,...) and m by ILAENV(5,...)
54 *> = 6: the crossover point for the SVD (when reducing an m by n
55 *> matrix to bidiagonal form, if max(m,n)/min(m,n) exceeds
56 *> this value, a QR factorization is used first to reduce
57 *> the matrix to a triangular form.)
58 *> = 7: the number of processors
59 *> = 8: the crossover point for the multishift QR and QZ methods
60 *> for nonsymmetric eigenvalue problems.
61 *> = 9: maximum size of the subproblems at the bottom of the
62 *> computation tree in the divide-and-conquer algorithm
63 *> =10: ieee NaN arithmetic can be trusted not to trap
64 *> =11: infinity arithmetic can be trusted not to trap
65 *>
66 *> Other specifications (up to 100) can be added later.
67 *> \endverbatim
68 *>
69 *> \param[in] NAME
70 *> \verbatim
71 *> NAME is CHARACTER*(*)
72 *> The name of the calling subroutine.
73 *> \endverbatim
74 *>
75 *> \param[in] OPTS
76 *> \verbatim
77 *> OPTS is CHARACTER*(*)
78 *> The character options to the subroutine NAME, concatenated
79 *> into a single character string. For example, UPLO = 'U',
80 *> TRANS = 'T', and DIAG = 'N' for a triangular routine would
81 *> be specified as OPTS = 'UTN'.
82 *> \endverbatim
83 *>
84 *> \param[in] N1
85 *> \verbatim
86 *> N1 is INTEGER
87 *> \endverbatim
88 *>
89 *> \param[in] N2
90 *> \verbatim
91 *> N2 is INTEGER
92 *> \endverbatim
93 *>
94 *> \param[in] N3
95 *> \verbatim
96 *> N3 is INTEGER
97 *> \endverbatim
98 *>
99 *> \param[in] N4
100 *> \verbatim
101 *> N4 is INTEGER
102 *>
103 *> Problem dimensions for the subroutine NAME; these may not all
104 *> be required.
105 *> \endverbatim
106 *>
107 *> \return ILAENV
108 *> \verbatim
109 *> ILAENV is INTEGER
110 *> >= 0: the value of the parameter specified by ISPEC
111 *> < 0: if ILAENV = -k, the k-th argument had an illegal value.
112 *> \endverbatim
113 *
114 * Authors:
115 * ========
116 *
117 *> \author Univ. of Tennessee
118 *> \author Univ. of California Berkeley
119 *> \author Univ. of Colorado Denver
120 *> \author NAG Ltd.
121 *
122 *> \date November 2011
123 *
124 *> \ingroup aux_lin
125 *
126 *> \par Further Details:
127 * =====================
128 *>
129 *> \verbatim
130 *>
131 *> The following conventions have been used when calling ILAENV from the
132 *> LAPACK routines:
133 *> 1) OPTS is a concatenation of all of the character options to
134 *> subroutine NAME, in the same order that they appear in the
135 *> argument list for NAME, even if they are not used in determining
136 *> the value of the parameter specified by ISPEC.
137 *> 2) The problem dimensions N1, N2, N3, N4 are specified in the order
138 *> that they appear in the argument list for NAME. N1 is used
139 *> first, N2 second, and so on, and unused problem dimensions are
140 *> passed a value of -1.
141 *> 3) The parameter value returned by ILAENV is checked for validity in
142 *> the calling subroutine. For example, ILAENV is used to retrieve
143 *> the optimal blocksize for STRTRI as follows:
144 *>
145 *> NB = ILAENV( 1, 'STRTRI', UPLO // DIAG, N, -1, -1, -1 )
146 *> IF( NB.LE.1 ) NB = MAX( 1, N )
147 *> \endverbatim
148 *>
149 * =====================================================================
150  INTEGER FUNCTION ilaenv( ISPEC, NAME, OPTS, N1, N2, N3,
151  $ n4 )
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 *
232  END