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DOUBLE PRECISION FUNCTION gsumln(a,b)
C-----------------------------------------------------------------------
C EVALUATION OF THE FUNCTION LN(GAMMA(A + B))
C FOR 1 .LE. A .LE. 2 AND 1 .LE. B .LE. 2
C-----------------------------------------------------------------------
C .. Scalar Arguments ..
DOUBLE PRECISION a,b
C ..
C .. Local Scalars ..
DOUBLE PRECISION x
C ..
C .. External Functions ..
DOUBLE PRECISION alnrel,gamln1
EXTERNAL alnrel,gamln1
C ..
C .. Intrinsic Functions ..
INTRINSIC dble,dlog
C ..
C .. Executable Statements ..
x = dble(a) + dble(b) - 2.D0
IF (x.GT.0.25D0) GO TO 10
gsumln = gamln1(1.0D0+x)
RETURN
10 IF (x.GT.1.25D0) GO TO 20
gsumln = gamln1(x) + alnrel(x)
RETURN
20 gsumln = gamln1(x-1.0D0) + dlog(x* (1.0D0+x))
RETURN
END
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