dlamch()

double precision function dlamch

(

character

cmach

)

Definition at line 1 of file dlamch.f.

*
*  -- LAPACK auxiliary routine (version 2.1) --
*     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
*     Courant Institute, Argonne National Lab, and Rice University
*     October 31, 1992
*
*     .. Scalar Arguments ..
      CHARACTER          CMACH
*     ..
*
*  Purpose
*  =======
*
*  DLAMCH determines double precision machine parameters.
*
*  Arguments
*  =========
*
*  CMACH   (input) CHARACTER*1
*          Specifies the value to be returned by DLAMCH:
*          = 'E' or 'e',   DLAMCH := eps
*          = 'S' or 's ,   DLAMCH := sfmin
*          = 'B' or 'b',   DLAMCH := base
*          = 'P' or 'p',   DLAMCH := eps*base
*          = 'N' or 'n',   DLAMCH := t
*          = 'R' or 'r',   DLAMCH := rnd
*          = 'M' or 'm',   DLAMCH := emin
*          = 'U' or 'u',   DLAMCH := rmin
*          = 'L' or 'l',   DLAMCH := emax
*          = 'O' or 'o',   DLAMCH := rmax
*
*          where
*
*          eps   = relative machine precision
*          sfmin = safe minimum, such that 1/sfmin does not overflow
*          base  = base of the machine
*          prec  = eps*base
*          t     = number of (base) digits in the mantissa
*          rnd   = 1.0 when rounding occurs in addition, 0.0 otherwise
*          emin  = minimum exponent before (gradual) underflow
*          rmin  = underflow threshold - base**(emin-1)
*          emax  = largest exponent before overflow
*          rmax  = overflow threshold  - (base**emax)*(1-eps)
*
* =====================================================================
*
*     .. Parameters ..
      DOUBLE PRECISION   ONE, ZERO
      parameter( one = 1.0d+0, zero = 0.0d+0 )
*     ..
*     .. Local Scalars ..
      LOGICAL            FIRST, LRND
      INTEGER            BETA, IMAX, IMIN, IT
      DOUBLE PRECISION   BASE, EMAX, EMIN, EPS, PREC, RMACH, RMAX, RMIN,
     $                   RND, SFMIN, SMALL, T
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           lsame
*     ..
*     .. External Subroutines ..
      EXTERNAL           dlamc2
*     ..
*     .. Save statement ..
      SAVE               first, eps, sfmin, base, t, rnd, emin, rmin,
     $                   emax, rmax, prec
*     ..
*     .. Data statements ..
      DATA               first / .true. /
*     ..
*     .. Executable Statements ..
*
      IF( first ) THEN
         first = .false.
         CALL dlamc2( beta, it, lrnd, eps, imin, rmin, imax, rmax )
         base = beta
         t = it
         IF( lrnd ) THEN
            rnd = one
            eps = ( base**( 1-it ) ) / 2
         ELSE
            rnd = zero
            eps = base**( 1-it )
         END IF
         prec = eps*base
         emin = imin
         emax = imax
         sfmin = rmin
         small = one / rmax
         IF( small.GE.sfmin ) THEN
*
*           Use SMALL plus a bit, to avoid the possibility of rounding
*           causing overflow when computing  1/sfmin.
*
            sfmin = small*( one+eps )
         END IF
      END IF
*
      IF( lsame( cmach, 'E' ) ) THEN
         rmach = eps
      ELSE IF( lsame( cmach, 'S' ) ) THEN
         rmach = sfmin
      ELSE IF( lsame( cmach, 'B' ) ) THEN
         rmach = base
      ELSE IF( lsame( cmach, 'P' ) ) THEN
         rmach = prec
      ELSE IF( lsame( cmach, 'N' ) ) THEN
         rmach = t
      ELSE IF( lsame( cmach, 'R' ) ) THEN
         rmach = rnd
      ELSE IF( lsame( cmach, 'M' ) ) THEN
         rmach = emin
      ELSE IF( lsame( cmach, 'U' ) ) THEN
         rmach = rmin
      ELSE IF( lsame( cmach, 'L' ) ) THEN
         rmach = emax
      ELSE IF( lsame( cmach, 'O' ) ) THEN
         rmach = rmax
      END IF
*
      dlamch = rmach
      RETURN
*
*     End of DLAMCH
*

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