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Make multinomial work for iterable input #170

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Make multinomial work for iterable input #170

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b0cb90a
make `multinomial` work for iterable input
thchr Nov 8, 2024
a67609a
fix test
thchr Nov 8, 2024
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12 changes: 7 additions & 5 deletions src/factorials.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -93,16 +93,18 @@ function primorial(n::Integer)
end

"""
multinomial(k...)
multinomial(k)
multinomial(k::Integer...)

Multinomial coefficient where `n = sum(k)`.
Multinomial coefficient ```(n, (k[1], k[2], … ))``` with `n = sum(k)`.
"""
function multinomial(k...)
s = 0
result = 1
function multinomial(k)
s = zero(eltype(k))
result = one(eltype(k))
@inbounds for i in k
s += i
result *= binomial(s, i)
end
result
end
multinomial(k::T...) where T<:Integer = multinomial(k)
2 changes: 2 additions & 0 deletions test/factorials.jl
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Expand Up @@ -33,6 +33,8 @@

# multinomial
@test multinomial(1, 4, 4, 2) == 34650
@test multinomial([1, 4, 4, 2]) == multinomial(1, 4, 4, 2)
@test (@inferred multinomial(big"1", big"4")) isa BigInt

# primorial
@test primorial(17) == 510510
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