1 2 FUNCTION ERFX(ARG) 3 !*********************************************************************** 4 ! ERFX Module of the AMS/EPA Regulatory Model - AERMOD 5 ! 6 ! PURPOSE: Calculates Error Function, Using Method Documented 7 ! on Page 187 of "Approximations for Digital Computers" 8 ! by Cecil Hastings, Princeton University Press, 1955 9 ! 10 ! PROGRAMMER: Roger Brode, Jeff Wang 11 ! 12 ! DATE: March 2, 1992 13 ! 14 ! INPUTS: Error Function Argument, ARG 15 ! 16 ! OUTPUTS: Error Function Value, ERFX 17 ! 18 ! CALLED FROM: PFRACT 19 !*********************************************************************** 20 21 ! Variable Declarations 22 IMPLICIT NONE 23 CHARACTER MODNAM*12 24 25 SAVE 26 DOUBLE PRECISION ARG , X , ERFX 27 28 ! Variable Initializations 29 MODNAM = 'ERFX' ! 0 30 31 IF ( ARG.GT.4.0 ) THEN 32 ERFX = 1.0 ! 0 33 ELSEIF ( ARG.LT.-4.0 ) THEN 34 ERFX = -1.0 ! 0 35 ELSEIF ( ABS(ARG).LT.1.0E-10 ) THEN 36 ERFX = 0.0 ! 0 37 ELSE 38 X = ABS(ARG) ! 0 39 ERFX = 1. - 1./(1.+X*(0.705230784E-1+X*(0.422820123E-1+X*( & 40 & 0.92705272E-2+ & 41 & X*(0.1520143E-3+X*(0.2765672E-3+X*0.430638E-4))))))**16. 42 IF ( ARG.LT.0.0 ) ERFX = -ERFX 43 ENDIF 44 45 CONTINUE ! 0 46 END
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