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Text File  |  1985-11-29  |  1.4 KB  |  50 lines
  1. C
  2. C     ..................................................................
  3. C
  4. C        SUBROUTINE QL5
  5. C
  6. C        PURPOSE
  7. C           TO COMPUTE INTEGRAL(EXP(-X)*FCT(X), SUMMED OVER X FROM 0
  8. C                               TO INFINITY).
  9. C
  10. C        USAGE
  11. C           CALL QL5 (FCT,Y)
  12. C           PARAMETER FCT REQUIRES AN EXTERNAL STATEMENT
  13. C
  14. C        DESCRIPTION OF PARAMETERS
  15. C           FCT    - THE NAME OF AN EXTERNAL FUNCTION SUBPROGRAM USED.
  16. C           Y      - THE RESULTING INTEGRAL VALUE.
  17. C
  18. C        REMARKS
  19. C           NONE
  20. C
  21. C        SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
  22. C           THE EXTERNAL FUNCTION SUBPROGRAM FCT(X) MUST BE FURNISHED
  23. C           BY THE USER.
  24. C
  25. C        METHOD
  26. C           EVALUATION IS DONE BY MEANS OF 5-POINT GAUSSIAN-LAGUERRE
  27. C           QUADRATURE FORMULA, WHICH INTEGRATES EXACTLY WHENEVER
  28. C           FCT(X) IS A POLYNOMIAL UP TO DEGREE 9.
  29. C           FOR REFERENCE, SEE
  30. C           V.I.KRYLOV, APPROXIMATE CALCULATION OF INTEGRALS,
  31. C           MACMILLAN, NEW YORK/LONDON, 1962, PP.130-132 AND 347-352.
  32. C
  33. C     ..................................................................
  34. C
  35.       SUBROUTINE QL5(FCT,Y)
  36. C
  37. C
  38.       X=12.64080
  39.       Y=.2336997E-4*FCT(X)
  40.       X=7.085810
  41.       Y=Y+.3611759E-2*FCT(X)
  42.       X=3.596426
  43.       Y=Y+.07594245*FCT(X)
  44.       X=1.413403
  45.       Y=Y+.3986668*FCT(X)
  46.       X=.2635603
  47.       Y=Y+.5217556*FCT(X)
  48.       RETURN
  49.       END
  50.