table of contents
dlamchf77.f(3) | LAPACK | dlamchf77.f(3) |
NAME¶
dlamchf77.f -SYNOPSIS¶
Functions/Subroutines¶
DOUBLE PRECISION function dlamch (CMACH)
Function/Subroutine Documentation¶
subroutine dlamc1 (integerBETA, integerT, logicalRND, logicalIEEE1)¶
DLAMC1 Purpose:DLAMC1 determines the machine parameters given by BETA, T, RND, and IEEE1.Parameters:
BETA
T
RND
IEEE1
Author:
The base of the machine.
The number of ( BETA ) digits in the mantissa.
Specifies whether proper rounding ( RND = .TRUE. ) or chopping ( RND = .FALSE. ) occurs in addition. This may not be a reliable guide to the way in which the machine performs its arithmetic.
Specifies whether rounding appears to be done in the IEEE 'round to nearest' style.
LAPACK is a software package provided by Univ.
of Tennessee, Univ. of California Berkeley, Univ. of Colorado Denver and NAG
Ltd..
Date:
April 2012
Further Details
The routine is based on the routine ENVRON by Malcolm and incorporates suggestions by Gentleman and Marovich. See Malcolm M. A. (1972) Algorithms to reveal properties of floating-point arithmetic. Comms. of the ACM, 15, 949-951. Gentleman W. M. and Marovich S. B. (1974) More on algorithms that reveal properties of floating point arithmetic units. Comms. of the ACM, 17, 276-277.
subroutine dlamc2 (integerBETA, integerT, logicalRND, double precisionEPS, integerEMIN, double precisionRMIN, integerEMAX, double precisionRMAX)¶
DLAMC2 Purpose:DLAMC2 determines the machine parameters specified in its argument list.
LAPACK is a software package provided by Univ.
of Tennessee, Univ. of California Berkeley, Univ. of Colorado Denver and NAG
Ltd..
Date:
April 2012
Parameters:
BETA
T
RND
EPS
EMIN
RMIN
EMAX
RMAX
Further Details
The base of the machine.
The number of ( BETA ) digits in the mantissa.
Specifies whether proper rounding ( RND = .TRUE. ) or chopping ( RND = .FALSE. ) occurs in addition. This may not be a reliable guide to the way in which the machine performs its arithmetic.
The smallest positive number such that fl( 1.0 - EPS ) .LT. 1.0, where fl denotes the computed value.
The minimum exponent before (gradual) underflow occurs.
The smallest normalized number for the machine, given by BASE**( EMIN - 1 ), where BASE is the floating point value of BETA.
The maximum exponent before overflow occurs.
The largest positive number for the machine, given by BASE**EMAX * ( 1 - EPS ), where BASE is the floating point value of BETA.
The computation of EPS is based on a routine PARANOIA by W. Kahan of the University of California at Berkeley.
DOUBLE PRECISION function dlamc3 (double precisionA, double precisionB)¶
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.Parameters:
A
B
The values A and B.
subroutine dlamc4 (integerEMIN, double precisionSTART, integerBASE)¶
DLAMC4 Purpose:DLAMC4 is a service routine for DLAMC2.Parameters:
EMIN
START
BASE
The minimum exponent before (gradual) underflow, computed by setting A = START and dividing by BASE until the previous A can not be recovered.
The starting point for determining EMIN.
The base of the machine.
subroutine dlamc5 (integerBETA, integerP, integerEMIN, logicalIEEE, integerEMAX, double precisionRMAX)¶
DLAMC5 Purpose:DLAMC5 attempts to compute RMAX, the largest machine floating-point number, without overflow. It assumes that EMAX + abs(EMIN) sum approximately to a power of 2. It will fail on machines where this assumption does not hold, for example, the Cyber 205 (EMIN = -28625, EMAX = 28718). It will also fail if the value supplied for EMIN is too large (i.e. too close to zero), probably with overflow.Parameters:
BETA
P
EMIN
IEEE
EMAX
RMAX
The base of floating-point arithmetic.
The number of base BETA digits in the mantissa of a floating-point value.
The minimum exponent before (gradual) underflow.
A logical flag specifying whether or not the arithmetic system is thought to comply with the IEEE standard.
The largest exponent before overflow
The largest machine floating-point number.
DOUBLE PRECISION function dlamch (characterCMACH)¶
DLAMCHF77 deprecated Purpose:DLAMCHF77 determines double precision machine parameters.
CMACH
Author:
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)
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
April 2012
Author¶
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