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DOUBLE PRECISION FUNCTION dbetrm(a,b)
C**********************************************************************
C
C DOUBLE PRECISION FUNCTION DBETRM( A, B )
C Double Precision Sterling Remainder for Complete
C Beta Function
C
C
C Function
C
C
C Log(Beta(A,B)) = Lgamma(A) + Lgamma(B) - Lgamma(A+B)
C where Lgamma is the log of the (complete) gamma function
C
C Let ZZ be approximation obtained if each log gamma is approximated
C by Sterling's formula, i.e.,
C Sterling(Z) = LOG( SQRT( 2*PI ) ) + ( Z-0.5 ) * LOG( Z ) - Z
C
C Returns Log(Beta(A,B)) - ZZ
C
C
C Arguments
C
C
C A --> One argument of the Beta
C DOUBLE PRECISION A
C
C B --> The other argument of the Beta
C DOUBLE PRECISION B
C
C**********************************************************************
C .. Scalar Arguments ..
DOUBLE PRECISION a,b
C ..
C .. External Functions ..
DOUBLE PRECISION dstrem
EXTERNAL dstrem
C ..
C .. Intrinsic Functions ..
INTRINSIC max,min
C ..
C .. Executable Statements ..
C Try to sum from smallest to largest
dbetrm = -dstrem(a+b)
dbetrm = dbetrm + dstrem(max(a,b))
dbetrm = dbetrm + dstrem(min(a,b))
RETURN
END
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