Function gmres_with_absolute_tolerance 

pub fn gmres_with_absolute_tolerance<T, F>(
    apply_a: F,
    b: &T,
    x0: &T,
    options: &GmresOptions,
    atol: f64,
) -> Result<GmresResult<T>>
where
    T: TensorVectorSpace,
    F: Fn(&T) -> Result<T>,

Solve A x = b using GMRES with an absolute residual tolerance.

This variant stops when ||b - A*x|| < atol. The default gmres API uses relative residual tolerance and is preferred for scale-independent solves.