D1MACH(3)

SYNOPSIS
DOUBLE PRECISION FUNCTION D1MACH (I)

NAME
d1mach - Return floating point machine dependent constants.

LIBRARY
SLATEC

CATEGORY
R1

TYPE
DOUBLE PRECISION (R1MACH-S, D1MACH-D)

KEYWORDS
MACHINE CONSTANTS

AUTHOR
Fox, P. A., (Bell Labs) Hall, A. D., (Bell Labs) Schryer, N. L., (Bell Labs)

DESCRIPTION
D1MACH can be used to obtain machine-dependent parameters for the local machine environment. It is a function subprogram with one (input) argument, and can be referenced as follows: D = D1MACH(I) where I=1,...,5. The (output) value of D above is determined by the (input) value of I. The results for various values of I are discussed below. D1MACH( 1) = B**(EMIN-1), the smallest positive magnitude. D1MACH( 2) = B**EMAX*(1 - B**(-T)), the largest magnitude. D1MACH( 3) = B**(-T), the smallest relative spacing. D1MACH( 4) = B**(1-T), the largest relative spacing. D1MACH( 5) = LOG10(B) Assume double precision numbers are represented in the T-digit, base-B form sign (B**E)*( (X(1)/B) + ... + (X(T)/B**T) ) where 0 .LE. X(I) .LT. B for I=1,...,T, 0 .LT. X(1), and EMIN .LE. E .LE. EMAX. The values of B, T, EMIN and EMAX are provided in I1MACH as follows: I1MACH(10) = B, the base. I1MACH(14) = T, the number of base-B digits. I1MACH(15) = EMIN, the smallest exponent E. I1MACH(16) = EMAX, the largest exponent E. To alter this function for a particular environment, the desired set of DATA statements should be activated by removing the C from column 1. Also, the values of D1MACH(1) - D1MACH(4) should be checked for consistency with the local operating system.

REFERENCES
P. A. Fox, A. D. Hall and N. L. Schryer, Framework for a portable library, ACM Transactions on Mathematical Software 4, 2 (June 1978), pp. 177-188.

ROUTINES CALLED
XERMSG

REVISION HISTORY (YYMMDD)
750101 DATE WRITTEN
890213 REVISION DATE from Version 3.2
891214 Prologue converted to Version 4.0 format. (BAB)
900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)
900618 Added DEC RISC constants. (WRB)
900723 Added IBM RS 6000 constants. (WRB)
900911 Added SUN 386i constants. (WRB)
910710 Added HP 730 constants. (SMR)
911114 Added Convex IEEE constants. (WRB)
920121 Added SUN -r8 compiler option constants. (WRB)
920229 Added Touchstone Delta i860 constants. (WRB)
920501 Reformatted the REFERENCES section. (WRB)
920625 Added CONVEX -p8 and -pd8 compiler option constants. (BKS, WRB)
930201 Added DEC Alpha and SGI constants. (RWC and WRB)