Function evaluate 

pub fn evaluate(
    graph: &FitGraphSpec,
    params_flat: &HashMap<String, f64>,
    x: &[f64],
) -> Result<Vec<f64>, CoreError>

Evaluate the model sum across all nodes at the given x-points.

params_flat keys follow the "node_id.param_name" convention.

Errors

Returns CoreError::Eval if: the graph fails to compile (unknown model type, missing parameter, duplicate node id, or a bad expr_edges cycle — see CompiledGraph::compile); params_flat is missing a "node_id.param_name" entry a node needs; x.len() is not an exact multiple of the graph’s coordinate dimensionality; or a node’s dataset_index is out of range for the compiled dataset_offsets.