nacfahi 0.3.7

Simpler, but less error-prone API for `levenberg-marquardt` optimization crate
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use crate::models::{FitModel, FitModelErrors, FitModelXDeriv};
use generic_array::GenericArray;
use num_traits::{One, Zero};
use typenum::U1;

/// Model representing a constant, independent of `x`
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Constant<Scalar> {
    /// The constant itself
    pub c: Scalar,
}

impl<Scalar: Clone + One> FitModel for Constant<Scalar> {
    type Scalar = Scalar;
    type ParamCount = U1;

    #[inline]
    fn evaluate(&self, _: &Self::Scalar) -> Self::Scalar {
        self.c.clone()
    }

    #[inline]
    fn jacobian(
        &self,
        _: &Self::Scalar,
    ) -> impl Into<GenericArray<Self::Scalar, Self::ParamCount>> {
        [Scalar::one()]
    }

    #[inline]
    fn set_params(&mut self, new_params: GenericArray<Self::Scalar, Self::ParamCount>) {
        let [new_c] = new_params.into_array();
        self.c = new_c;
    }

    #[inline]
    fn get_params(&self) -> impl Into<GenericArray<Self::Scalar, Self::ParamCount>> {
        [self.c.clone()]
    }
}

impl<Scalar: Clone + Zero + One> FitModelXDeriv for Constant<Scalar> {
    #[inline]
    fn deriv_x(&self, _: &Self::Scalar) -> Scalar {
        Scalar::zero()
    }
}

impl<Scalar: 'static> FitModelErrors for Constant<Scalar>
where
    Self: FitModel<Scalar = Scalar, ParamCount = U1>,
{
    type OwnedModel = Self;

    #[inline]
    fn with_errors(errors: GenericArray<Self::Scalar, Self::ParamCount>) -> Self::OwnedModel {
        let [c] = errors.into_array();
        Self { c }
    }
}

#[cfg(test)]
mod tests;