src/coefficients.rs

Mon, 24 Oct 2022 10:52:19 +0300

author
Tuomo Valkonen <tuomov@iki.fi>
date
Mon, 24 Oct 2022 10:52:19 +0300
changeset 4
61b068c50e25
parent 0
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child 5
59dc4c5883f4
permissions
-rw-r--r--

Added type for numerical errors

0
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1 ///! This module implements some arithmetic functions that are valid in a ‘const context”, i.e.,
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2 ///! can be computed at compile-time.
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3
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4 /// Calculate $n!$.
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5 /// (The version in the crate `num_integer` deesn't currently work in a `const` context.
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6 pub const fn factorial(n : usize) -> usize {
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7 const fn f(i : usize, a : usize) -> usize {
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8 if i==0 { a } else { f(i-1, i*a) }
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9 }
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10 f(n, 1)
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11 }
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12
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13 /// Calculate $\nchoosek{n}{k}$.
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14 /// (The version in the crate `num_integer` deesn't currently work in a `const` context.
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15 pub const fn binomial(n : usize, k : usize) -> usize {
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16 factorial(n)/(factorial(n-k)*factorial(k))
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17 }
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18
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19 /// Calculate $n^k$.
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20 /// (The version in the crate `num_integer` deesn't currently work in a `const` context.
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21 pub const fn pow(n : usize, k : usize) -> usize {
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22 const fn pow_accum(n : usize, k : usize, accum : usize) -> usize {
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23 if k==0 { accum } else { pow_accum(n, k-1, accum*n) }
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24 }
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25 pow_accum(n, k, 1)
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26 }

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