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Text File  |  1985-11-29  |  2KB  |  61 lines
  1. C
  2. C     ..................................................................
  3. C
  4. C        SUBROUTINE DQA8
  5. C
  6. C        PURPOSE
  7. C           TO COMPUTE INTEGRAL(EXP(-X)*FCT(X)/SQRT(X), SUMMED OVER X
  8. C                               FROM 0 TO INFINITY).
  9. C
  10. C        USAGE
  11. C           CALL DQA8 (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 DOUBLE PRECISION FUNCTION
  16. C                    SUBPROGRAM USED.
  17. C           Y      - THE RESULTING DOUBLE PRECISION INTEGRAL VALUE.
  18. C
  19. C        REMARKS
  20. C           NONE
  21. C
  22. C        SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
  23. C           THE EXTERNAL DOUBLE PRECISION FUNCTION SUBPROGRAM FCT(X)
  24. C           MUST BE FURNISHED BY THE USER.
  25. C
  26. C        METHOD
  27. C           EVALUATION IS DONE BY MEANS OF 8-POINT GENERALIZED GAUSS-
  28. C           LAGUERRE QUADRATURE FORMULA, WHICH INTEGRATES EXACTLY
  29. C           WHENEVER FCT(X) IS A POLYNOMIAL UP TO DEGREE 15.
  30. C           FOR REFERENCE, SEE
  31. C           SHAO/CHEN/FRANK, TABLES OF ZEROS AND GAUSSIAN WEIGHTS OF
  32. C           CERTAIN ASSOCIATED LAGUERRE POLYNOMIALS AND THE RELATED
  33. C           GENERALIZED HERMITE POLYNOMIALS, IBM TECHNICAL REPORT
  34. C           TR00.1100 (MARCH 1964), PP.15-16.
  35. C
  36. C     ..................................................................
  37. C
  38.       SUBROUTINE DQA8(FCT,Y)
  39. C
  40. C
  41.       DOUBLE PRECISION X,Y,FCT
  42. C
  43.       X=.21984272840962651D2
  44.       Y=.53096149480223645D-9*FCT(X)
  45.       X=.14972627088426393D2
  46.       Y=Y+.46419616897304213D-6*FCT(X)
  47.       X=.10093323675221343D2
  48.       Y=Y+.54237201850757630D-4*FCT(X)
  49.       X=.64831454286271704D1
  50.       Y=Y+.18645680172483611D-2*FCT(X)
  51.       X=.38094763614849071D1
  52.       Y=Y+.25760623071019947D-1*FCT(X)
  53.       X=.19051136350314284D1
  54.       Y=Y+.16762008279797166D0*FCT(X)
  55.       X=.67724908764928915D0
  56.       Y=Y+.56129491705706735D0*FCT(X)
  57.       X=.7479188259681827D-1
  58.       Y=Y+.10158589580332275D1*FCT(X)
  59.       RETURN
  60.       END
  61.