Throw error for invalid log_frequency values (#665)

src/algorithm.jl

@@ -880,7 +880,7 @@ Train the policy for `model`.
    progress. Defaults to `SDDP.log`.
 
  - `log_frequency::Int`: control the frequency with which the logging is
-    outputted (iterations/log). Defaults to `1`.
+    outputted (iterations/log). It must be at least `1`. Defaults to `1`.
 
  - `log_every_seconds::Float64`: control the frequency with which the logging is
    outputted (seconds/log). Defaults to `0.0`.
@@ -965,6 +965,10 @@ function train(
     forward_pass_callback::Function = (x) -> nothing,
     post_iteration_callback = result -> nothing,
 )
+    if log_frequency <= 0
+        msg = "`log_frequency` must be at least `1`. Got $log_frequency."
+        throw(ArgumentError(msg))
+    end
     function log_frequency_f(log::Vector{Log})
         if mod(length(log), log_frequency) != 0
             return false

test/algorithm.jl

@@ -327,6 +327,19 @@ function test_print_log()
     return
 end
 
+function test_log_frequency_argument_error()
+    model = SDDP.LinearPolicyGraph(
+        stages = 2,
+        lower_bound = 0.0,
+        optimizer = HiGHS.Optimizer,
+    ) do node, stage
+        @variable(node, x >= 0, SDDP.State, initial_value = 0.0)
+        @stageobjective(node, x.out)
+    end
+    @test_throws ArgumentError SDDP.train(model; log_frequency = 0)
+    return
+end
+
 end  # module
 
 TestAlgorithm.runtests()