dlamch.f File Reference

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Functions/Subroutines
double precision function	dlamch (cmach)
	DLAMCH
double precision function	dlamc3 (a, b)
	DLAMC3

Function/Subroutine Documentation

dlamc3()

double precision function dlamc3	(	double precision	a,
		double precision	b )

DLAMC3

Purpose:

!> DLAMC3  is intended to force  A  and  B  to be stored prior to doing
!> the addition of  A  and  B ,  for use in situations where optimizers
!> might hold one of these in a register.
!> 

Author

LAPACK is a software package provided by Univ. of Tennessee, Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..

Parameters

[in]	A	!> A is a DOUBLE PRECISION !>
[in]	B	!> B is a DOUBLE PRECISION !> The values A and B. !>

Definition at line 168 of file dlamch.f.

*
*  -- LAPACK auxiliary routine --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*
*     .. Scalar Arguments ..
      DOUBLE PRECISION   A, B
*     ..
* =====================================================================
*
*     .. Executable Statements ..
*
      dlamc3 = a + b
*
      RETURN
*
*     End of DLAMC3
*

dlamch()

double precision function dlamch

(

character

cmach

)

DLAMCH

Purpose:

!>
!> DLAMCH determines double precision machine parameters.
!> 

Parameters

[in]

CMACH

!> CMACH is 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) !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 68 of file dlamch.f.

*
*  -- LAPACK auxiliary routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      CHARACTER          CMACH
*     ..
*
* =====================================================================
*
*     .. Parameters ..
      DOUBLE PRECISION   ONE, ZERO
      parameter( one = 1.0d+0, zero = 0.0d+0 )
*     ..
*     .. Local Scalars ..
      DOUBLE PRECISION   RND, EPS, SFMIN, SMALL, RMACH
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           lsame
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          digits, epsilon, huge, maxexponent,
     $                   minexponent, radix, tiny
*     ..
*     .. Executable Statements ..
*
*
*     Assume rounding, not chopping. Always.
*
      rnd = one
*
      IF( one.EQ.rnd ) THEN
         eps = epsilon(zero) * 0.5
      ELSE
         eps = epsilon(zero)
      END IF
*
      IF( lsame( cmach, 'E' ) ) THEN
         rmach = eps
      ELSE IF( lsame( cmach, 'S' ) ) THEN
         sfmin = tiny(zero)
         small = one / huge(zero)
         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
         rmach = sfmin
      ELSE IF( lsame( cmach, 'b' ) ) THEN
         RMACH = RADIX(ZERO)
      ELSE IF( LSAME( CMACH, 'p' ) ) THEN
         RMACH = EPS * RADIX(ZERO)
      ELSE IF( LSAME( CMACH, 'n' ) ) THEN
         RMACH = DIGITS(ZERO)
      ELSE IF( LSAME( CMACH, 'r' ) ) THEN
         RMACH = RND
      ELSE IF( LSAME( CMACH, 'm' ) ) THEN
         RMACH = MINEXPONENT(ZERO)
      ELSE IF( LSAME( CMACH, 'u' ) ) THEN
         RMACH = tiny(zero)
      ELSE IF( LSAME( CMACH, 'l' ) ) THEN
         RMACH = MAXEXPONENT(ZERO)
      ELSE IF( LSAME( CMACH, 'o' ) ) THEN
         RMACH = HUGE(ZERO)
      ELSE
         RMACH = ZERO
      END IF
*
      DLAMCH = RMACH
      RETURN
*
*     End of DLAMCH
*