Total output steps inconsistent with inputs when using multiple monitors with higher frequency

[ZedThree]

I think there's a bug in the current implementation in master and next, or at least behaviour that I find surprising. I've modified the monitor example to print the name of the monitor for clarity, and got this output (on next):

Custom output monitor fast, time = 0.000000e+00, step -1 of 20

Custom output monitor default, time = 0.000000e+00, step -1 of 10
Sim Time  |  RHS evals  | Wall Time |  Calc    Inv   Comm    I/O   SOLVER

0.000e+00          1       4.33e-02    -1.3    0.0    1.6  147.2  -47.4
|  Step 1 of 10. Elapsed 0:00:00.0 ETA 0:00:00.3
Custom output monitor fast, time = 1.000000e+00, step 0 of 10

Custom output monitor fast, time = 2.000000e+00, step 1 of 10

Custom output monitor default, time = 2.000000e+00, step 0 of 5
2.000e+00         92       6.33e-02     5.8    0.0    0.0   50.6   43.6
/  Step 1 of 5. Elapsed 0:00:00.1 ETA 0:00:00.1
Custom output monitor fast, time = 3.000000e+00, step 2 of 10

Custom output monitor fast, time = 4.000000e+00, step 3 of 10

Custom output monitor default, time = 4.000000e+00, step 1 of 5
4.000e+00         41       5.49e-02     4.1    0.0    0.0   45.3   50.7
-  Step 2 of 5. Elapsed 0:00:00.2 ETA 0:00:00.1
Custom output monitor fast, time = 5.000000e+00, step 4 of 10

Custom output monitor fast, time = 6.000000e+00, step 5 of 10

Custom output monitor default, time = 6.000000e+00, step 2 of 5
6.000e+00         44       5.48e-02     3.5    0.0    0.0   46.1   50.3
\  Step 3 of 5. Elapsed 0:00:00.2 ETA 0:00:00.0
Custom output monitor fast, time = 7.000000e+00, step 6 of 10

Custom output monitor fast, time = 8.000000e+00, step 7 of 10

Custom output monitor default, time = 8.000000e+00, step 3 of 5
8.000e+00         41       5.24e-02     3.7    0.0    0.0   45.3   51.0
|  Step 4 of 5. Elapsed 0:00:00.3 ETA 0:00:-0.1
Custom output monitor fast, time = 9.000000e+00, step 8 of 10

Custom output monitor fast, time = 1.000000e+01, step 9 of 10

Custom output monitor default, time = 1.000000e+01, step 4 of 5
1.000e+01         44       5.80e-02     4.2    0.0    0.0   42.8   53.0
/  Step 5 of 5. Elapsed 0:00:00.3 ETA 0:00:-0.1

This is with nout = 10 and timestep = 1. Although the simulation runs to sim time nout * timestep and the relative frequencies of the monitors are all correct, notice that there are only 5 output steps that happen with timestep = 2.

I think the fix is:

modified   src/solver/solver.cxx
@@ -498,6 +498,9 @@ int Solver::solve(int nout, BoutReal timestep) {
 
   finaliseMonitorPeriods(nout, timestep);
 
+  number_output_steps = nout;
+  output_timestep = timestep;
+
   output_progress.write(
       _("Solver running for {:d} outputs with output timestep of {:e}\n"), nout,
       timestep);

This then runs for 10 output steps with timestep = 1, which is what I expect at least

Originally posted by @ZedThree in #2882 (comment)