18 lines
487 B
Forth
18 lines
487 B
Forth
import: math
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[
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676.5203681218851, -1259.1392167224028, 771.32342877765313,
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-176.61502916214059, 12.507343278686905, -0.13857109526572012,
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9.9843695780195716e-6, 1.5056327351493116e-7
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] const: Gamma.Lanczos
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: gamma(z)
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| i t |
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z 0.5 < ifTrue: [ Pi dup z * sin 1.0 z - gamma * / return ]
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z 1.0 - ->z
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0.99999999999980993 Gamma.Lanczos size loop: i [ i Gamma.Lanczos at z i + / + ]
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z Gamma.Lanczos size + 0.5 - ->t
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2 Pi * sqrt *
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t z 0.5 + powf *
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t neg exp * ;
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