hypergeometric.rs

fn main () {
    println!("{}", hg(1,8,3,4));
}

fn hg(a: i64, b: i64, c: i64, z: i64) -> i64 {
    let mut j = 10;
    loop {
        let snp1 = inner_hg(a,b,c,z,j+1);
        let sn = inner_hg(a,b,c,z,j);
        if (((snp1 - sn).abs() / sn) as f64) < 0.001f64 {
            return sn;
        }
        else {
            j = j+1;
        }
    }
}

fn inner_hg(a: i64, b: i64, c: i64, z: i64, j: i64) -> i64 {
    if (j == -1) || (j==0) {
        1
    }
    else if j == 1 {
        ((a*b*z)/c)
    }
    else {
        let rj = ((a+j-1)*(b+j-1))/(j*(c+j-1));
        let sj1 = inner_hg(a,b,c,z,j-1);
        return sj1 + (sj1 - inner_hg(a,b,c,z,j-2))*rj*z;
    }
}

A very inefficient implementation of the hypergeometric function in rust