ganit_core/eval/functions/math/multinomial/
mod.rs

1use crate::eval::coercion::to_number;
2use crate::eval::functions::check_arity;
3use crate::types::{ErrorKind, Value};
4
5/// `MULTINOMIAL(value1, value2, ...)` — (sum of args)! / product of factorials of each arg.
6pub fn multinomial_fn(args: &[Value]) -> Value {
7    if let Some(err) = check_arity(args, 1, usize::MAX) {
8        return err;
9    }
10    let mut values: Vec<u64> = Vec::with_capacity(args.len());
11    for arg in args {
12        let n = match to_number(arg.clone()) {
13            Err(e) => return e,
14            Ok(v) => v,
15        };
16        if n < 0.0 {
17            return Value::Error(ErrorKind::Num);
18        }
19        values.push(n.trunc() as u64);
20    }
21    let sum: u64 = values.iter().sum();
22    // Compute sum! / product(i!) using the identity:
23    // MULTINOMIAL = C(sum, v1) * C(sum-v1, v2) * ...
24    let mut result = 1.0f64;
25    let mut remaining = sum;
26    for &v in &values {
27        result *= combinations(remaining, v);
28        remaining -= v;
29    }
30    Value::Number(result)
31}
32
33fn combinations(n: u64, k: u64) -> f64 {
34    if k == 0 || k == n {
35        return 1.0;
36    }
37    let k = k.min(n - k);
38    let mut result = 1.0f64;
39    for i in 0..k {
40        result *= (n - i) as f64;
41        result /= (i + 1) as f64;
42    }
43    result
44}
45
46#[cfg(test)]
47mod tests;
ganit_core/eval/functions/math/multinomial/mod.rs

ganit_core/eval/functions/math/multinomial/
mod.rs
