Function utsolve 

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

Solves U’x=b where x and b are dense.

x=b on input, solution on output.

Example:

let u = [
    vec![0.9842, 0.1720, 0.9948, 0.2766, 0.4560, 0.1462, 0.8124],
    vec![0.0000, 0.6894, 0.1043, 0.4486, 0.5217, 0.7157, 0.4132],
    vec![0.0000, 0.0000, -0.5500, -0.2340, 0.0822, 0.2176, -0.1996],
    vec![0.0000, 0.0000, 0.0000, 0.6554, -0.1564, -0.0287, 0.2107],
    vec![0.0000, 0.0000, 0.0000, 0.0000, -0.4127, -0.4652, -0.6993],
    vec![0.0000, 0.0000, 0.0000, 0.0000, 0.0000, 0.6881, 0.3037],
    vec![0.0000, 0.0000, 0.0000, 0.0000, 0.0000, 0.0000, -0.7740]
];
let mut u_sparse = rsparse::data::Sprs::new();
u_sparse.from_vec(&u);

let mut b = [
    0.444841,
    0.528773,
    0.988345,
    0.097749,
    0.996166,
    0.068040,
    0.844511
];

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