ilaenv.f

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      INTEGER          FUNCTION ILAENV( ISPEC, NAME, OPTS, N1, N2, N3,
     $                 N4 )
*
*  -- LAPACK auxiliary routine (version 3.1) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     .. 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( 1, 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( 0, 0.0, 1.0 )
         END IF
*
      ELSE
*
*        Invalid value for ISPEC
*
         ILAENV = -1
      END IF
*
      RETURN
*
*     End of ILAENV
*
      END