mirror of
https://git.planet-casio.com/Lephenixnoir/OpenLibm.git
synced 2025-01-01 06:23:39 +01:00
83 lines
3.5 KiB
Fortran
83 lines
3.5 KiB
Fortran
*DECK DERF
|
|
DOUBLE PRECISION FUNCTION DERF (X)
|
|
C***BEGIN PROLOGUE DERF
|
|
C***PURPOSE Compute the error function.
|
|
C***LIBRARY SLATEC (FNLIB)
|
|
C***CATEGORY C8A, L5A1E
|
|
C***TYPE DOUBLE PRECISION (ERF-S, DERF-D)
|
|
C***KEYWORDS ERF, ERROR FUNCTION, FNLIB, SPECIAL FUNCTIONS
|
|
C***AUTHOR Fullerton, W., (LANL)
|
|
C***DESCRIPTION
|
|
C
|
|
C DERF(X) calculates the double precision error function for double
|
|
C precision argument X.
|
|
C
|
|
C Series for ERF on the interval 0. to 1.00000E+00
|
|
C with weighted error 1.28E-32
|
|
C log weighted error 31.89
|
|
C significant figures required 31.05
|
|
C decimal places required 32.55
|
|
C
|
|
C***REFERENCES (NONE)
|
|
C***ROUTINES CALLED D1MACH, DCSEVL, DERFC, INITDS
|
|
C***REVISION HISTORY (YYMMDD)
|
|
C 770701 DATE WRITTEN
|
|
C 890531 Changed all specific intrinsics to generic. (WRB)
|
|
C 890531 REVISION DATE from Version 3.2
|
|
C 891214 Prologue converted to Version 4.0 format. (BAB)
|
|
C 900727 Added EXTERNAL statement. (WRB)
|
|
C 920618 Removed space from variable name. (RWC, WRB)
|
|
C***END PROLOGUE DERF
|
|
DOUBLE PRECISION X, ERFCS(21), SQEPS, SQRTPI, XBIG, Y, D1MACH,
|
|
1 DCSEVL, DERFC
|
|
LOGICAL FIRST
|
|
EXTERNAL DERFC
|
|
SAVE ERFCS, SQRTPI, NTERF, XBIG, SQEPS, FIRST
|
|
DATA ERFCS( 1) / -.4904612123 4691808039 9845440333 76 D-1 /
|
|
DATA ERFCS( 2) / -.1422612051 0371364237 8247418996 31 D+0 /
|
|
DATA ERFCS( 3) / +.1003558218 7599795575 7546767129 33 D-1 /
|
|
DATA ERFCS( 4) / -.5768764699 7674847650 8270255091 67 D-3 /
|
|
DATA ERFCS( 5) / +.2741993125 2196061034 4221607914 71 D-4 /
|
|
DATA ERFCS( 6) / -.1104317550 7344507604 1353812959 05 D-5 /
|
|
DATA ERFCS( 7) / +.3848875542 0345036949 9613114981 74 D-7 /
|
|
DATA ERFCS( 8) / -.1180858253 3875466969 6317518015 81 D-8 /
|
|
DATA ERFCS( 9) / +.3233421582 6050909646 4029309533 54 D-10 /
|
|
DATA ERFCS( 10) / -.7991015947 0045487581 6073747085 95 D-12 /
|
|
DATA ERFCS( 11) / +.1799072511 3961455611 9672454866 34 D-13 /
|
|
DATA ERFCS( 12) / -.3718635487 8186926382 3168282094 93 D-15 /
|
|
DATA ERFCS( 13) / +.7103599003 7142529711 6899083946 66 D-17 /
|
|
DATA ERFCS( 14) / -.1261245511 9155225832 4954248533 33 D-18 /
|
|
DATA ERFCS( 15) / +.2091640694 1769294369 1705002666 66 D-20 /
|
|
DATA ERFCS( 16) / -.3253973102 9314072982 3641600000 00 D-22 /
|
|
DATA ERFCS( 17) / +.4766867209 7976748332 3733333333 33 D-24 /
|
|
DATA ERFCS( 18) / -.6598012078 2851343155 1999999999 99 D-26 /
|
|
DATA ERFCS( 19) / +.8655011469 9637626197 3333333333 33 D-28 /
|
|
DATA ERFCS( 20) / -.1078892517 7498064213 3333333333 33 D-29 /
|
|
DATA ERFCS( 21) / +.1281188399 3017002666 6666666666 66 D-31 /
|
|
DATA SQRTPI / 1.772453850 9055160272 9816748334 115D0 /
|
|
DATA FIRST /.TRUE./
|
|
C***FIRST EXECUTABLE STATEMENT DERF
|
|
IF (FIRST) THEN
|
|
NTERF = INITDS (ERFCS, 21, 0.1*REAL(D1MACH(3)))
|
|
XBIG = SQRT(-LOG(SQRTPI*D1MACH(3)))
|
|
SQEPS = SQRT(2.0D0*D1MACH(3))
|
|
ENDIF
|
|
FIRST = .FALSE.
|
|
C
|
|
Y = ABS(X)
|
|
IF (Y.GT.1.D0) GO TO 20
|
|
C
|
|
C ERF(X) = 1.0 - ERFC(X) FOR -1.0 .LE. X .LE. 1.0
|
|
C
|
|
IF (Y.LE.SQEPS) DERF = 2.0D0*X*X/SQRTPI
|
|
IF (Y.GT.SQEPS) DERF = X*(1.0D0 + DCSEVL (2.D0*X*X-1.D0,
|
|
1 ERFCS, NTERF))
|
|
RETURN
|
|
C
|
|
C ERF(X) = 1.0 - ERFC(X) FOR ABS(X) .GT. 1.0
|
|
C
|
|
20 IF (Y.LE.XBIG) DERF = SIGN (1.0D0-DERFC(Y), X)
|
|
IF (Y.GT.XBIG) DERF = SIGN (1.0D0, X)
|
|
C
|
|
RETURN
|
|
END
|