Struct CountsModel 

pub struct CountsModel<'a> {
    pub transmission_model: &'a dyn FitModel,
    pub flux: &'a [f64],
    pub background: &'a [f64],
    pub n_params: usize,
}

Fixed-flux counts-domain forward model: Y_model = flux × T_model(θ) + background.

Retained for the research Fisher helper, not for production fitting. The production counts-KL dispatch (SolverConfig::PoissonKL on InputData::Counts / InputData::CountsWithNuisance) goes through the joint-Poisson conditional-binomial-deviance path in crate::joint_poisson per memo 35 §P1/§P2. CountsModel and CountsBackgroundScaleModel below are consumed only by nereids_pipeline::pipeline::evaluate_jacobian_and_fisher (the Fisher-info research helper used by the spatial-regularization epic #394) and by this module’s #[cfg(test)] tests. They assume the caller has pre-computed flux = c · O (i.e. c is baked into flux — the convention that memo 35 §P1 flagged as error-prone for end users, which is precisely why the production path no longer uses this struct).

The flux and background slices must have the same length as the transmission vector returned by the inner model. In debug builds, evaluate() asserts this invariant.

Fields

transmission_model: &'a dyn FitModel

Underlying transmission model.

flux: &'a [f64]

Incident flux (counts per bin in open beam, after normalization).

background: &'a [f64]

Background counts per bin.

n_params: usize

Total parameter count in the wrapped model.

Trait Implementations

impl<'a> FitModel for CountsModel<'a>

fn analytical_jacobian( &self, params: &[f64], free_param_indices: &[usize], y_current: &[f64], ) -> Option<FlatMatrix>

Analytical Jacobian: ∂Y/∂θ = flux · ∂T_inner/∂θ.

Background is constant w.r.t. θ and drops out.

fn evaluate(&self, params: &[f64]) -> Result<Vec<f64>, FittingError>

Evaluate the model for the given parameters.

impl<'a> ForwardModel for CountsModel<'a>

fn predict(&self, params: &[f64]) -> Result<Vec<f64>, FittingError>

Predict model output for the given parameter vector.

fn n_data(&self) -> usize

Number of data points in the model output.

fn n_params(&self) -> usize

Number of parameters (total, including fixed).

fn jacobian( &self, _params: &[f64], _free_param_indices: &[usize], _y_current: &[f64], ) -> Option<Vec<Vec<f64>>>

Analytical Jacobian (column-major layout).