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2329
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1 *DECK DERF |
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2 DOUBLE PRECISION FUNCTION DERF (X) |
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3 C***BEGIN PROLOGUE DERF |
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4 C***PURPOSE Compute the error function. |
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5 C***LIBRARY SLATEC (FNLIB) |
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6 C***CATEGORY C8A, L5A1E |
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7 C***TYPE DOUBLE PRECISION (ERF-S, DERF-D) |
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8 C***KEYWORDS ERF, ERROR FUNCTION, FNLIB, SPECIAL FUNCTIONS |
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9 C***AUTHOR Fullerton, W., (LANL) |
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10 C***DESCRIPTION |
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11 C |
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12 C DERF(X) calculates the double precision error function for double |
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13 C precision argument X. |
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14 C |
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15 C Series for ERF on the interval 0. to 1.00000E+00 |
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16 C with weighted error 1.28E-32 |
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17 C log weighted error 31.89 |
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18 C significant figures required 31.05 |
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19 C decimal places required 32.55 |
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20 C |
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21 C***REFERENCES (NONE) |
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22 C***ROUTINES CALLED D1MACH, DCSEVL, DERFC, INITDS |
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23 C***REVISION HISTORY (YYMMDD) |
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24 C 770701 DATE WRITTEN |
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25 C 890531 Changed all specific intrinsics to generic. (WRB) |
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26 C 890531 REVISION DATE from Version 3.2 |
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27 C 891214 Prologue converted to Version 4.0 format. (BAB) |
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28 C 900727 Added EXTERNAL statement. (WRB) |
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29 C 920618 Removed space from variable name. (RWC, WRB) |
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30 C***END PROLOGUE DERF |
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31 DOUBLE PRECISION X, ERFCS(21), SQEPS, SQRTPI, XBIG, Y, D1MACH, |
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32 1 DCSEVL, DERFC |
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33 LOGICAL FIRST |
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34 EXTERNAL DERFC |
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35 SAVE ERFCS, SQRTPI, NTERF, XBIG, SQEPS, FIRST |
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36 DATA ERFCS( 1) / -.4904612123 4691808039 9845440333 76 D-1 / |
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37 DATA ERFCS( 2) / -.1422612051 0371364237 8247418996 31 D+0 / |
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38 DATA ERFCS( 3) / +.1003558218 7599795575 7546767129 33 D-1 / |
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39 DATA ERFCS( 4) / -.5768764699 7674847650 8270255091 67 D-3 / |
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40 DATA ERFCS( 5) / +.2741993125 2196061034 4221607914 71 D-4 / |
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41 DATA ERFCS( 6) / -.1104317550 7344507604 1353812959 05 D-5 / |
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42 DATA ERFCS( 7) / +.3848875542 0345036949 9613114981 74 D-7 / |
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43 DATA ERFCS( 8) / -.1180858253 3875466969 6317518015 81 D-8 / |
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44 DATA ERFCS( 9) / +.3233421582 6050909646 4029309533 54 D-10 / |
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45 DATA ERFCS( 10) / -.7991015947 0045487581 6073747085 95 D-12 / |
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46 DATA ERFCS( 11) / +.1799072511 3961455611 9672454866 34 D-13 / |
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47 DATA ERFCS( 12) / -.3718635487 8186926382 3168282094 93 D-15 / |
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48 DATA ERFCS( 13) / +.7103599003 7142529711 6899083946 66 D-17 / |
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49 DATA ERFCS( 14) / -.1261245511 9155225832 4954248533 33 D-18 / |
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50 DATA ERFCS( 15) / +.2091640694 1769294369 1705002666 66 D-20 / |
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51 DATA ERFCS( 16) / -.3253973102 9314072982 3641600000 00 D-22 / |
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52 DATA ERFCS( 17) / +.4766867209 7976748332 3733333333 33 D-24 / |
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53 DATA ERFCS( 18) / -.6598012078 2851343155 1999999999 99 D-26 / |
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54 DATA ERFCS( 19) / +.8655011469 9637626197 3333333333 33 D-28 / |
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55 DATA ERFCS( 20) / -.1078892517 7498064213 3333333333 33 D-29 / |
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56 DATA ERFCS( 21) / +.1281188399 3017002666 6666666666 66 D-31 / |
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57 DATA SQRTPI / 1.772453850 9055160272 9816748334 115D0 / |
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58 DATA FIRST /.TRUE./ |
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59 C***FIRST EXECUTABLE STATEMENT DERF |
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60 IF (FIRST) THEN |
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61 NTERF = INITDS (ERFCS, 21, 0.1*REAL(D1MACH(3))) |
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62 XBIG = SQRT(-LOG(SQRTPI*D1MACH(3))) |
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63 SQEPS = SQRT(2.0D0*D1MACH(3)) |
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64 ENDIF |
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65 FIRST = .FALSE. |
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66 C |
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67 Y = ABS(X) |
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68 IF (Y.GT.1.D0) GO TO 20 |
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69 C |
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70 C ERF(X) = 1.0 - ERFC(X) FOR -1.0 .LE. X .LE. 1.0 |
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71 C |
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72 IF (Y.LE.SQEPS) DERF = 2.0D0*X*X/SQRTPI |
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73 IF (Y.GT.SQEPS) DERF = X*(1.0D0 + DCSEVL (2.D0*X*X-1.D0, |
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74 1 ERFCS, NTERF)) |
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75 RETURN |
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76 C |
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77 C ERF(X) = 1.0 - ERFC(X) FOR ABS(X) .GT. 1.0 |
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78 C |
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79 20 IF (Y.LE.XBIG) DERF = SIGN (1.0D0-DERFC(Y), X) |
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80 IF (Y.GT.XBIG) DERF = SIGN (1.0D0, X) |
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81 C |
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82 RETURN |
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83 END |
