Constant functions

Now we've implemented the rhs function, but how about the initial condition? We can implement the ConstantOp trait to specify the initial condition. Since this is quite similar to the NonLinearOp trait, we will do it all in one go.

use crate::{C, M, T, V};
use diffsol::{ConstantOp, Op, Vector};

pub struct MyInit<'a> {
    pub p: &'a V,
}

impl Op for MyInit<'_> {
    type T = T;
    type V = V;
    type M = M;
    type C = C;
    fn nstates(&self) -> usize {
        1
    }
    fn nout(&self) -> usize {
        1
    }
    fn nparams(&self) -> usize {
        0
    }
    fn context(&self) -> &Self::C {
        self.p.context()
    }
}

impl ConstantOp for MyInit<'_> {
    fn call_inplace(&self, _t: T, y: &mut V) {
        y[0] = 0.1;
    }
}