Add failing test cases for flatness check

Author: timholy

test/captured.jl

@@ -21,15 +21,47 @@ end
     end
 end
 
-# From PR#174
-@testset "PR#174" begin
-    tc = LineSearchTestCase(
-        [0.0, 1.0, 5.0, 3.541670844449739],
-        [3003.592409634743, 2962.0378569864743, 2891.4462095232184, 3000.9760725116876],
-        [-22332.321416890798, -20423.214551925797, 11718.185026267562, -22286.821227217057]
-    )
-    fdf = OnceDifferentiable(tc)
-    hz = HagerZhang()
-    α, val = hz(fdf.f, fdf.fdf, 1.0, fdf.fdf(0.0)...)
-    @test_broken val <= minimum(tc)
+wolfec1(ls::BackTracking) = ls.c_1
+wolfec1(ls::StrongWolfe) = ls.c_1
+wolfec1(ls::MoreThuente) = ls.f_tol
+wolfec1(ls::HagerZhang{T}) where T = zero(T)  # HZ uses Wolfe condition, but not necessarily based at zero
+
+function amongtypes(x, types)
+    t = typeof(x)
+    return any(t <: ty for ty in types)
+end
+
+@testset "Captured cases" begin
+    lsalgs =  (HagerZhang(), StrongWolfe(), MoreThuente(),
+               BackTracking(), BackTracking(; order=2) )
+    # From PR#174
+    @testset "PR#174" begin
+        tc = LineSearchTestCase(
+            [0.0, 1.0, 5.0, 3.541670844449739],
+            [3003.592409634743, 2962.0378569864743, 2891.4462095232184, 3000.9760725116876],
+            [-22332.321416890798, -20423.214551925797, 11718.185026267562, -22286.821227217057]
+        )
+        fdf = OnceDifferentiable(tc)
+        for ls in lsalgs
+            α, val = ls(fdf.f, fdf.df, fdf.fdf, 1.0, fdf.fdf(0.0)...)
+            @test 0 < α <= 5
+            @test val < fdf.f(0) + wolfec1(ls) * α * fdf.df(0)   # Armijo (first Wolfe) condition
+            if amongtypes(ls, (StrongWolfe, MoreThuente, HagerZhang))  # these types do not just backtrack
+                @test val <= tc.values[2]
+            end
+        end
+    end
+    @testset "Issue#175" begin
+        tc = LineSearchTestCase(
+            [0.0, 0.2, 0.1, 0.055223623837026156],
+            [3.042968312396456, 3.1174112871667603, -3.5035848233450224, 0.5244246783151265],
+            [-832.4270136930788, -505.3362249257043, 674.9478303586366, 738.3388472427769]
+        )
+        fdf = OnceDifferentiable(tc)
+        for ls in lsalgs
+            α, val = ls(fdf.f, fdf.df, fdf.fdf, 0.2, fdf.fdf(0.0)...)
+            @test 0 < α < 0.2
+            @test val < fdf.f(0) + wolfec1(ls) * α * fdf.df(0)
+        end
+    end
 end