RosettaCodeData/Task/Gamma-function/BBC-BASIC/gamma-function.basic

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*FLOAT64
INSTALL @lib$+"FNUSING"
FOR x = 0.1 TO 2.05 STEP 0.1
PRINT FNusing("#.#",x), FNusing("##.############", FNgamma(x))
NEXT
END
DEF FNgamma(z) = EXP(FNlngamma(z))
DEF FNlngamma(z)
LOCAL a, b, i%, lz()
DIM lz(6)
lz() = 1.000000000190015, 76.18009172947146, -86.50532032941677, \
\ 24.01409824083091, -1.231739572450155, 0.0012086509738662, -0.000005395239385
IF z < 0.5 THEN = LN(PI / SIN(PI * z)) - FNlngamma(1.0 - z)
z -= 1.0
b = z + 5.5
a = lz(0)
FOR i% = 1 TO 6
a += lz(i%) / (z + i%)
NEXT
= (LNSQR(2*PI) + LN(a) - b) + LN(b) * (z+0.5)