| 1 | FUNCTION GAMFCN(W,T,TAU1,TAU2) |
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| 2 | IMPLICIT REAL (A-H,O-Z) |
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| 3 | C |
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| 4 | C COMPUTES THE LINE SHAPE FOR PRESSURE-INDUCED H2-H2 AND H2-HE |
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| 5 | C TRANSITIONS, FROM THE SEMI-EMIRICAL FORMULAE OF BIRNBAUM ET AL. |
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| 6 | C SEE EG., GEORGE BIRNBAUM AND E. RICHARD COHEN, CANADIAN JOURNAL |
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| 7 | C OF PHYSICS, VOL. 54, 593 (1976). |
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| 8 | C NOTE THAT "GAMFCN" IS A POOR NAME FOR THIS ROUTINE; THE GAMMA |
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| 9 | C OF BIRNBAUM AND COHEN IS NOT THE USUAL "GAMMA FUNCTION". |
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| 10 | C |
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| 11 | save hk,pi,tau10,tau20 |
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| 12 | DATA HK/7.638315E-12/,PI/3.141593/,TAU10/0.0/,TAU20/0.0/ |
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| 13 | logical first |
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| 14 | data first/.true./ |
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| 15 | save first |
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| 16 | |
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| 17 | C NOTE: HK = 1.05450E-27 / 1.38054E-16 |
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| 18 | C |
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| 19 | C*********************************************************************** |
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| 20 | save tau12,z2,hbh |
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| 21 | |
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| 22 | if (first) |
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| 23 | s print*,'WARNING!!! ON rajoute des valeurs a 0.', |
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| 24 | s 'Est-ce bien raisonable... dans GAMFCN' |
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| 25 | first=.false. |
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| 26 | IF (TAU1 .NE. TAU10) GO TO 10 |
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| 27 | IF (TAU2 .EQ. TAU20) GO TO 20 |
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| 28 | 10 TAU12 = TAU1 * TAU1 |
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| 29 | TAU22 = TAU2 * TAU2 |
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| 30 | HBH = 0.5 * HK / T |
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| 31 | Z2 = SQRT(TAU22 + HBH**2) / TAU1 |
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| 32 | TAU10 = TAU1 |
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| 33 | TAU20 = TAU2 |
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| 34 | 20 WSQR = W * W |
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| 35 | Z = SQRT(1.0+WSQR*TAU12) * Z2 |
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| 36 | IF (Z .LE. 1.0) GO TO 50 |
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| 37 | C COMPUTE K1 BESSEL FUNCTION USING POLYNOMIAL APPROXIMATION |
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| 38 | A = 1.0 / Z |
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| 39 | BK1 = 1.253314 + .4699927*A |
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| 40 | B = A * A |
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| 41 | BK1 = BK1 - .1468583*B |
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| 42 | B = B * A |
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| 43 | BK1 = BK1 + .1280427*B |
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| 44 | B = B * A |
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| 45 | BK1 = BK1 - .1736432*B |
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| 46 | B = B * A |
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| 47 | BK1 = BK1 + .2847618*B |
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| 48 | B = B * A |
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| 49 | BK1 = BK1 - .4594342*B |
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| 50 | B = B * A |
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| 51 | BK1 = BK1 + .6283381*B |
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| 52 | B = B * A |
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| 53 | BK1 = BK1 - .6632295*B |
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| 54 | B = B * A |
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| 55 | BK1 = BK1 + .5050239*B |
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| 56 | B = B * A |
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| 57 | BK1 = BK1 - .2581304*B |
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| 58 | B = B * A |
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| 59 | BK1 = BK1 + .7880001E-01*B |
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| 60 | B = B * A |
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| 61 | BK1 = BK1 - .1082418E-01*B |
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| 62 | BK1 = EXP(-Z) * BK1 * SQRT(A) |
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| 63 | GO TO 100 |
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| 64 | C COMPUTE K1 BESSEL FUNCTION USING SERIES EXPANSION |
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| 65 | 50 A = 0.5 * Z |
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| 66 | B = .5772157 + LOG(A) |
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| 67 | C = A * A |
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| 68 | BK1 = 1.0/Z + A*(B-0.5) |
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| 69 | A = A * C |
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| 70 | BK1 = BK1 + A*.2500000E+00*(0.5+(B-1.500000)*2.0) |
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| 71 | A = A * C |
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| 72 | BK1 = BK1 + A*.2777777E-01*(0.5+(B-1.833333)*3.0) |
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| 73 | A = A * C |
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| 74 | BK1 = BK1 + A*.1736110E-02*(0.5+(B-2.083333)*4.0) |
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| 75 | A = A * C |
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| 76 | BK1 = BK1 + A*.6944439E-04*(0.5+(B-2.283333)*5.0) |
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| 77 | A = A * C |
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| 78 | BK1 = BK1 + A*.1929009E-05*(0.5+(B-2.449999)*6.0) |
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| 79 | A = A * C |
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| 80 | BK1 = BK1 + A*.3936752E-07*(0.5+(B-2.592855)*7.0) |
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| 81 | A = A * C |
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| 82 | BK1 = BK1 + A*.6151173E-09*(0.5+(B-2.717855)*8.0) |
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| 83 | 100 CONTINUE |
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| 84 | GAMFCN = TAU1/PI * EXP(TAU2/TAU1+HBH*W) * Z*BK1 / (1.0+WSQR*TAU12) |
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| 85 | RETURN |
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| 86 | END |
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