fix: Only calculate the summary in inner loop

Calculating the summary both inside and outside the loop in
`take_steps!` is inconsistent.
This shows up as discontinuities in quantities such as the energy
because the kinetic and gravitational energy are out of phase by half a
time step.

The fix: calculate summaries only in the inner loop.  Any summary
quantities that depend on the phase should be calculated carefully,
potentially with a temporary update to psi by half a time step.

BREAKING CHANGE: summary is calculated at slightly different times

Project.toml

@@ -1,7 +1,7 @@
 name = "UltraDark"
 uuid = "1c8d022d-dfc0-4b41-80ab-3fc7e88cdfea"
 authors = ["Nathan Musoke <[email protected]>"]
-version = "0.2.2"
+version = "0.3.0"
 
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"

src/UltraDark.jl

@@ -25,6 +25,14 @@ import .Output: output_summary_row, output_summary_header, output_grids, output_
 import .Output: SummaryStatistics, SummaryStatisticsMeanMaxRms
 import .Config: SimulationConfig, constant_scale_factor, TimeStepOptions
 
+"""
+    outer_step!(Δt, grids, constants; a=1.0)
+
+Perform the "outer" time step in the symmetrized split-step Fourier method.
+
+This step only updates the phase of ψ applying accelerations due to gravity,
+the amplitude is not changed.
+"""
 function outer_step!(Δt, grids, constants; a=1.0)
     psi_whole_step!(Δt, grids, constants)
 end
@@ -53,6 +61,13 @@ function psi_whole_step!(Δt, grids, constants)
     end
 end
 
+"""
+    inner_step!(Δt, grids, constants; a=1.0)
+
+Perform the "inner" time step in the symmetrized split-step Fourier method.
+
+This step applies the diffusion terms and updates the gravitational potential.
+"""
 function inner_step!(Δt, grids, constants; a=1.0)
     phi_whole_step!(Δt, grids, constants; a=1.0)
 end
@@ -145,8 +160,6 @@ function take_steps!(grids, t_start, Δt, n, output_config, a, constants)
     outer_step!(Δt/2, grids, constants)
     t += Δt / 2
 
-    output_summary_row(grids, output_config, t, a(t), Δt)
-
     t
 end