!DECK D1MACH DOUBLE PRECISION FUNCTION D1MACH (I) IMPLICIT NONE INTEGER :: I DOUBLE PRECISION :: B, X !***BEGIN PROLOGUE D1MACH !***PURPOSE Return floating point machine dependent constants. !***LIBRARY SLATEC !***CATEGORY R1 !***TYPE SINGLE PRECISION (D1MACH-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: ! ! A = D1MACH(I) ! ! where I=1,...,5. The (output) value of A 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 single 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(11) = T, the number of base-B digits. ! I1MACH(12) = EMIN, the smallest exponent E. ! I1MACH(13) = EMAX, the largest exponent E. ! ! !***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) ! 790101 DATE WRITTEN ! 960329 Modified for Fortran 90 (BE after suggestions by EHG) !***END PROLOGUE D1MACH ! X = 1.0D0 B = RADIX(X) SELECT CASE (I) CASE (1) D1MACH = B**(MINEXPONENT(X)-1) ! the smallest positive magnitude. CASE (2) D1MACH = HUGE(X) ! the largest magnitude. CASE (3) D1MACH = B**(-DIGITS(X)) ! the smallest relative spacing. CASE (4) D1MACH = B**(1-DIGITS(X)) ! the largest relative spacing. CASE (5) D1MACH = LOG10(B) CASE DEFAULT WRITE (*, FMT = 9000) 9000 FORMAT ('1ERROR 1 IN D1MACH - I OUT OF BOUNDS') STOP END SELECT RETURN END