Function evaluate 

pub fn evaluate(
    expr: &Expr,
    inputs: &dyn FormulaInputs,
    time: usize,
    depth: usize,
) -> Result<Slice2D>

Evaluate expr at the given time and layer indices into a displayable slice.

Missing or fill cells in any input stay missing; non-finite results from the arithmetic itself (e.g. log of a negative value) are reported as NaN/±Inf so domain errors remain visible.