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/*!
Forward models from discrete measures to observations.
*/

use alg_tools::error::DynError;
use alg_tools::euclidean::Euclidean;
use alg_tools::instance::Instance;
pub use alg_tools::linops::*;
use alg_tools::norms::{Norm, NormExponent, L2};

use crate::measures::Radon;
use crate::types::*;
pub mod bias;
pub mod sensor_grid;

/// `ForwardeModel`s are bounded preadjointable linear operators  $A ∈ 𝕃(𝒵(Ω); E)$
/// where $𝒵(Ω) ⊂ ℳ(Ω)$ is the space of sums of delta measures, presented by
/// [`crate::measures::DiscreteMeasure`], and $E$ is a [`Euclidean`] space.
pub trait ForwardModel<Domain: Space, F: Float = f64, E: NormExponent = Radon>:
    BoundedLinear<Domain, E, L2, F, Codomain = Self::Observable>
    + GEMV<F, Domain, Self::Observable>
    + Preadjointable<Domain, Self::Observable>
where
    for<'a> Self::Observable: Instance<Self::Observable>,
    Domain: Norm<F, E>,
{
    /// The codomain or value space (of “observables”) for this operator.
    /// It is assumed to be a [`Euclidean`] space, and therefore also (identified with)
    /// the domain of the preadjoint.
    type Observable: Euclidean<F, Output = Self::Observable> + AXPY<F> + Space + Clone;

    /// Write an observable into a file.
    fn write_observable(&self, b: &Self::Observable, prefix: String) -> DynError;

    /// Returns a zero observable
    fn zero_observable(&self) -> Self::Observable;
}

/// Trait for operators $A$ for which $A_*A$ is bounded by some other operator.
pub trait AdjointProductBoundedBy<Domain: Space, D>: Linear<Domain> {
    type FloatType: Float;
    /// Return $L$ such that $A_*A ≤ LD$.
    fn adjoint_product_bound(&self, other: &D) -> Option<Self::FloatType>;
}

/// Trait for operators $A$ for which $A_*A$ is bounded by a diagonal operator.
pub trait AdjointProductPairBoundedBy<Domain: Space, D1, D2>: Linear<Domain> {
    type FloatType: Float;
    /// Return $(L, L_z)$ such that $A_*A ≤ (L_1 D_1, L_2 D_2)$.
    fn adjoint_product_pair_bound(
        &self,
        other1: &D1,
        other_2: &D2,
    ) -> Option<(Self::FloatType, Self::FloatType)>;
}

/*
/// Trait for [`ForwardModel`]s whose preadjoint has Lipschitz values.
pub trait LipschitzValues {
    type FloatType : Float;
    /// Return (if one exists) a factor $L$ such that $A_*z$ is $L$-Lipschitz for all
    /// $z$ in the unit ball.
    fn value_unit_lipschitz_factor(&self) -> Option<Self::FloatType> {
        None
    }

    /// Return (if one exists) a factor $L$ such that $∇A_*z$ is $L$-Lipschitz for all
    /// $z$ in the unit ball.
    fn value_diff_unit_lipschitz_factor(&self) -> Option<Self::FloatType> {
        None
    }
}
*/

/// Trait for [`ForwardModel`]s that satisfy bounds on curvature.
pub trait BoundedCurvature {
    type FloatType: Float;

    /// Returns factor $ℓ_F$ and $ℓ_r$ such that
    /// $B_{F'(μ)} dγ ≤ ℓ_F c_2$ and $⟨F'(μ)+F'(μ+Δ)|Δ⟩ ≤ ℓ_r|γ|(c_2)$,
    /// where $Δ=(π_♯^1-π_♯^0)γ$.
    fn curvature_bound_components(&self) -> (Option<Self::FloatType>, Option<Self::FloatType>);
}