added: error logging when no solution available

Author: franckgaga

docs/Project.toml

@@ -4,8 +4,11 @@ DAQP = "c47d62df-3981-49c8-9651-128b1cd08617"
 Documenter = "e30172f5-a6a5-5a46-863b-614d45cd2de4"
 JuMP = "4076af6c-e467-56ae-b986-b466b2749572"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
+Logging = "56ddb016-857b-54e1-b83d-db4d58db5568"
 Plots = "91a5bcdd-55d7-5caf-9e0b-520d859cae80"
 
 [compat]
 ControlSystemsBase = "1"
 Documenter = "1"
+LinearAlgebra = "1.6"
+Logging = "1.6"

docs/src/manual/nonlinmpc.md

@@ -114,6 +114,7 @@ We test `mpc` performance on `plant` by imposing an angular setpoint of 180° (i
 position):
 
 ```@example 1
+using Logging; disable_logging(Warn) # hide
 res_ry = sim!(nmpc, N, [180.0], plant=plant, x0=[0, 0], x̂0=[0, 0, 0])
 plot(res_ry)
 savefig(ans, "plot3_NonLinMPC.svg"); nothing # hide

src/predictive_control.jl

@@ -726,11 +726,18 @@ function optim_objective!(mpc::PredictiveController)
         end
     end
     status = termination_status(optim)
+    ΔŨcurr, ΔŨlast = value.(ΔŨvar), ΔŨ0
     if !(status == OPTIMAL || status == LOCALLY_SOLVED)
-        @warn "MPC termination status not OPTIMAL or LOCALLY_SOLVED ($status)"
+        if isfatal(status)
+            @error("MPC terminated without solution: returning last solution shifted", 
+                   status, ΔŨcurr, ΔŨlast)
+        else
+            @warn("MPC termination status not OPTIMAL or LOCALLY_SOLVED: keeping "*
+                  "solution anyway", status, ΔŨcurr, ΔŨlast)
+        end
         @debug solution_summary(optim, verbose=true)
     end
-    mpc.ΔŨ[:] = isfatal(status) ? ΔŨ0 : value.(ΔŨvar) # fatal status : use last value
+    mpc.ΔŨ[:] = isfatal(status) ? ΔŨlast : ΔŨcurr
     return mpc.ΔŨ
 end