sprs: Compilation error with CsMat and generic Float

I am new to sprs library, I do not understand why the following program does not compile:

use num_traits::Float;
use sprs::CsMat;

fn test<F: Float>(val: F) -> CsMat<F> {
    let a = CsMat::new_csc(
        (3, 3),
        vec![0, 2, 4, 5],
        vec![0, 1, 0, 2, 2],
        vec![val, val, val, val, val],
    );
    let b = &a + &a;
    b
}

fn main() {
    let a = test(1.);
}

with the following dependencies

[dependencies]
sprs = "0.10"
num-traits = "0.2"

and when I try to build I get:

error[E0369]: cannot add `&CsMatBase<F, usize, Vec<usize>, Vec<usize>, Vec<F>>` to `&CsMatBase<F, usize, Vec<usize>, Vec<usize>, Vec<F>>`
  --> src\main.rs:11:16
   |
11 |     let b = &a + &a;
   |             -- ^ -- &CsMatBase<F, usize, Vec<usize>, Vec<usize>, Vec<F>>
   |             |
   |             &CsMatBase<F, usize, Vec<usize>, Vec<usize>, Vec<F>>

error: aborting due to previous error

For more information about this error, try `rustc --explain E0369`.
error: could not compile `test-sprs`

To learn more, run the command again with --verbose.

I cannot see what is missing to enable the addition. Thanks for your help.