Sources Esope | Cast3M

endw2
C ENDW2     SOURCE    CHAT      05/01/12    23:39:24     5004
      FUNCTION ENDW2 (N,ALPHA,BETA)
      IMPLICIT INTEGER(I-N)
      IMPLICIT REAL*8(A-H,O-Z)
      ZERO  = 0.D0
      ONE   = 1.D0
      TWO   = 2.D0
      THREE = 3.D0
      FOUR  = 4.D0
      APB   = ALPHA+BETA
      IF (N.EQ.0) THEN
         ENDW2 = ZERO
         RETURN
      ENDIF
      F1   = GAMMAF(ALPHA+ONE)*GAMMAF(BETA+TWO)/GAMMAF(APB+THREE)
      F1   = F1*(APB+TWO)*TWO**(APB+TWO)/TWO
      IF (N.EQ.1) THEN
         ENDW2 = F1
         RETURN
      ENDIF
      FINT1 = GAMMAF(ALPHA+ONE)*GAMMAF(BETA+TWO)/GAMMAF(APB+THREE)
      FINT1 = FINT1*TWO**(APB+TWO)
      FINT2 = GAMMAF(ALPHA+TWO)*GAMMAF(BETA+TWO)/GAMMAF(APB+FOUR)
      FINT2 = FINT2*TWO**(APB+THREE)
      F2    = (TWO*(ALPHA+TWO)*FINT1 - (APB+FOUR)*FINT2)
     $        * (APB+THREE)/FOUR
      IF (N.EQ.2) THEN
         ENDW2 = F2
         RETURN
      ENDIF
      DO 100 I=3,N
         DI   = DBLE(I-1)
         ABN  = ALPHA+BETA+DI
         ABNN = ABN+DI
         A1   =  -(TWO*(DI+ALPHA)*(DI+BETA))/(ABN*ABNN*(ABNN+ONE))
         A2   =  (TWO*(ALPHA-BETA))/(ABNN*(ABNN+TWO))
         A3   =  (TWO*(ABN+ONE))/((ABNN+TWO)*(ABNN+ONE))
         F3   =  -(A2*F2+A1*F1)/A3
         F1   = F2
         F2   = F3
 100  CONTINUE
      ENDW2  = F3
      RETURN
      END