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INTEGER FUNCTION ILAENV( ISPEC, NAME, OPTS, N1, N2, N3,
$ N4 )
*
* -- LAPACK auxiliary routine (version 3.0) --
* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
* Courant Institute, Argonne National Lab, and Rice University
* June 30, 1999
*
* .. Scalar Arguments ..
CHARACTER*( * ) NAME, OPTS
INTEGER ISPEC, N1, N2, N3, N4
* ..
*
* 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.
*
* Arguments
* =========
*
* ISPEC (input) 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.
*
* NAME (input) CHARACTER*(*)
* The name of the calling subroutine.
*
* OPTS (input) 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'.
*
* N1 (input) INTEGER
* N2 (input) INTEGER
* N3 (input) INTEGER
* N4 (input) INTEGER
* Problem dimensions for the subroutine NAME; these may not all
* be required.
*
* (ILAENV) (output) INTEGER
* >= 0: the value of the parameter specified by ISPEC
* < 0: if ILAENV = -k, the k-th argument had an illegal value.
*
* 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 )
*
* =====================================================================
*
* .. Intrinsic Functions ..
INTRINSIC INT, MIN, REAL
* ..
* .. External Functions ..
INTEGER IEEECK
EXTERNAL IEEECK
* ..
* .. Arrays in Common ..
INTEGER IPARMS( 100 )
* ..
* .. Common blocks ..
COMMON / CLAENV / IPARMS
* ..
* .. Save statement ..
SAVE / CLAENV /
* ..
* .. Executable Statements ..
*
IF( ISPEC.GE.1 .AND. ISPEC.LE.5 ) THEN
*
* Return a value from the common block.
*
ILAENV = IPARMS( ISPEC )
*
ELSE IF( ISPEC.EQ.6 ) THEN
*
* Compute SVD crossover point.
*
ILAENV = INT( REAL( MIN( N1, N2 ) )*1.6E0 )
*
ELSE IF( ISPEC.GE.7 .AND. ISPEC.LE.9 ) THEN
*
* Return a value from the common block.
*
ILAENV = IPARMS( ISPEC )
*
ELSE IF( ISPEC.EQ.10 ) THEN
*
* IEEE NaN arithmetic can be trusted not to trap
*
C ILAENV = 0
ILAENV = 1
IF( ILAENV.EQ.1 ) THEN
ILAENV = IEEECK( 0, 0.0, 1.0 )
END IF
*
ELSE IF( ISPEC.EQ.11 ) THEN
*
* Infinity arithmetic can be trusted not to trap
*
C ILAENV = 0
ILAENV = 1
IF( ILAENV.EQ.1 ) THEN
ILAENV = IEEECK( 1, 0.0, 1.0 )
END IF
*
ELSE
*
* Invalid value for ISPEC
*
ILAENV = -1
END IF
*
RETURN
*
* End of ILAENV
*
END
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