From 116730d01f3549b129c9117b1437355c22c70d83 Mon Sep 17 00:00:00 2001
From: Michael Friedlander <michael@friedlander.io>
Date: Sun, 6 Oct 2024 09:32:15 -0700
Subject: [PATCH] Ensure that the preconditioner is pos def.

This doesn't seem to be a great preconditioner, but it does test the precon option.
---
 test/runtests.jl | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/test/runtests.jl b/test/runtests.jl
index 3eb0c48e..52d49958 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -82,11 +82,12 @@ end
 @testset "Preconditioner in Trunk" begin
   x0 = [-1.2; 1.0]
   nlp = ADNLPModel(x -> 100 * (x[2] - x[1]^2)^2 + (x[1] - 1)^2, x0)
-  DiagPrecon(x) = Diagonal(inv( [200 + 800 * x[1]^2 - 400 * x[2]  0.0;
-                               0.0                              200] ))
-
+  function DiagPrecon(x)
+     H = Matrix(hess(nlp, x))
+     λmin = minimum(eigvals(H))
+     Diagonal(H + λmin * I)
+  end 
   M = DiagPrecon(x0)
-  # implement `ldiv!` for `Diagonal` to avoid copying
   function LinearAlgebra.ldiv!(y, M::Diagonal, x)
     y .= M \ x
   end
@@ -95,5 +96,4 @@ end
   end
   stats = trunk(nlp, callback=callback, M=M)
   @test stats.status == :first_order
-
 end
\ No newline at end of file