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Text File  |  1985-11-29  |  1KB  |  44 lines
  1. C
  2. C     ..................................................................
  3. C
  4. C        SUBROUTINE QL2
  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 QL2 (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 2-POINT GAUSSIAN-LAGUERRE
  27. C           QUADRATURE FORMULA, WHICH INTEGRATES EXACTLY WHENEVER
  28. C           FCT(X) IS A POLYNOMIAL UP TO DEGREE 3.
  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 QL2(FCT,Y)
  36. C
  37. C
  38.       X=3.414214
  39.       Y=.1464466*FCT(X)
  40.       X=.5857864
  41.       Y=Y+.8535534*FCT(X)
  42.       RETURN
  43.       END
  44.