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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 |