Function usolve 

pub fn usolve<T: Numeric<T>>(u: &Sprs<T>, x: &mut [T])

Solves an upper triangular system. Solves U*x=b.

Solve Ux=b where x and b are dense. x=b on input, solution on output.

Example:

let u = [
    vec![0.7824, 0.4055, 0.0827, 0.9534, 0.9713, 0.1418, 0.0781],
    vec![0.0, 0.7766, 0.2981, 0.2307, -0.3172, 0.6819, 0.5979],
    vec![0.0, 0.0, 0.2986, -0.5576, 0.5928, -0.2759, -0.1672],
    vec![0.0, 0.0, 0.0, 0.6393, -0.4245, 0.1277, 0.5842],
    vec![0.0, 0.0, 0.0, 0.0, -1.277, 1.1435, 1.0631],
    vec![0.0, 0.0, 0.0, 0.0, 0.0, 1.2096, 0.7268],
    vec![0.0, 0.0, 0.0, 0.0, 0.0, 0.0, -0.4574]
];
let mut u_sparse = rsparse::data::Sprs::new();
u_sparse.from_vec(&u);

let mut b = [
    0.189772,
    0.055761,
    0.030676,
    0.181620,
    0.526924,
    0.744179,
    0.078005
];

rsparse::usolve(&u_sparse, &mut b);