debug: sometimes allow setmodel! on MPC based on SteadyKalmanFilter and Luenberger

Allow it if and only if the plant model and the covariance matrices do not change.
This allow calling `setmodel!` on `mpc` to modify the weights but nothing else.

Author: franckgaga

src/estimator/kalman.jl

@@ -199,9 +199,12 @@ function SteadyKalmanFilter(
     return SteadyKalmanFilter{NT, SM}(model, i_ym, nint_u, nint_ym, Q̂, R̂; direct)
 end
 
-"Throw an error if `setmodel!` is called on a SteadyKalmanFilter"
-function setmodel_estimator!(::SteadyKalmanFilter, args...)
-    error("SteadyKalmanFilter does not support setmodel! (use KalmanFilter instead)")
+"Throw an error if `setmodel!` is called on a SteadyKalmanFilter w/o the default values."
+function setmodel_estimator!(estim::SteadyKalmanFilter, model, _ , _ , _ , Q̂, R̂)
+    if estim.model !== model || !isnothing(Q̂) || !isnothing(R̂)
+        error("SteadyKalmanFilter does not support setmodel! (use KalmanFilter instead)")
+    end
+    return nothing
 end
 
 @doc raw"""

src/estimator/luenberger.jl

@@ -135,5 +135,10 @@ function update_estimate!(estim::Luenberger, y0m, d0, u0)
     return predict_estimate_obsv!(estim, y0m, d0, u0)
 end
 
-"Throw an error if `setmodel!` is called on `Luenberger` observer."
-setmodel_estimator!(::Luenberger, args...) = error("Luenberger does not support setmodel!")
+"Throw an error if `setmodel!` is called on `Luenberger` observer w/o the default values."
+function setmodel!(estim::Luenberger, model, args...)
+    if estim.model !== model
+        error("Luenberger does not support setmodel!")
+    end
+    return nothing
+end