From 3c848e1ae4ba0665ed9f214845dffe8f93713a9d Mon Sep 17 00:00:00 2001
From: Nathan Musoke <nathan.musoke@unh.edu>
Date: Fri, 29 Apr 2022 12:10:44 -0400
Subject: [PATCH] feat: Add volume of grid cells

Add a function dV that calculates the volume of the individual grid
cells.
---
 Project.toml     |  2 +-
 src/UltraDark.jl |  1 +
 src/grids.jl     | 26 ++++++++++++++++++++++++++
 test/grids.jl    |  6 ++++++
 4 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/Project.toml b/Project.toml
index 8d528ae..4460d34 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "UltraDark"
 uuid = "1c8d022d-dfc0-4b41-80ab-3fc7e88cdfea"
 authors = ["Nathan Musoke <n.musoke@auckland.ac.nz>"]
-version = "0.4.0"
+version = "0.4.1"
 
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"
diff --git a/src/UltraDark.jl b/src/UltraDark.jl
index 87d531f..59438f9 100644
--- a/src/UltraDark.jl
+++ b/src/UltraDark.jl
@@ -9,6 +9,7 @@ using FFTW
 
 export simulate
 export Grids, PencilGrids
+export dV
 export Config, SimulationConfig, constant_scale_factor, TimeStepOptions
 export OutputConfig
 export SummaryStatistics, SummaryStatisticsMeanMaxRms
diff --git a/src/grids.jl b/src/grids.jl
index 5b1c75d..4455371 100644
--- a/src/grids.jl
+++ b/src/grids.jl
@@ -271,3 +271,29 @@ function rk_norm(lengths, resols)
 
     (kx.^2 .+ ky.^2 .+ kz.^2).^0.5
 end
+
+"""
+    dV(grids)
+
+Calculate the volume of each grid cell
+
+# Examples
+
+```jldoctest
+julia> using UltraDark
+
+julia> box_length = 1.0;
+
+julia> resol = 16;
+
+julia> g = Grids(box_length, resol);
+
+julia> dV(g) * resol^3 == box_length^3
+true
+
+```
+
+"""
+function dV(grids)
+    diff(grids.x, dims=1)[1] * diff(grids.y, dims=2)[1] * diff(grids.z, dims=3)[1]
+end
diff --git a/test/grids.jl b/test/grids.jl
index 6f1b59a..095eaba 100644
--- a/test/grids.jl
+++ b/test/grids.jl
@@ -14,12 +14,16 @@ for grids_type in [Grids, PencilGrids]
         @test reshape(grids.x, resol) == reshape(grids.y, resol)
         @test reshape(grids.x, resol) == reshape(grids.z, resol)
 
+        @test dV(grids) * resol^3 == 1.0^3
+
         grids = grids_type((1.0, 1.0, 1.0), (resol, resol, resol))
         @test typeof(grids) <: grids_type
         @test all(grids.ψx .== 0)
         @test reshape(grids.x, resol) == reshape(grids.y, resol)
         @test reshape(grids.x, resol) == reshape(grids.z, resol)
 
+        @test dV(grids) * resol^3 == 1.0^3
+
         grids = grids_type((4.0, 2.0, 1.0), (4resol, 2resol, 1resol))
         @test typeof(grids) <: grids_type
         @test all(grids.ψx .== 0)
@@ -28,6 +32,8 @@ for grids_type in [Grids, PencilGrids]
         @test size(grids.z) == (1, 1, 1resol)
         @test reshape(grids.x, 4resol)[1 + 4resol÷2 - 4resol÷8:4resol÷2 + 4resol÷8] == reshape(grids.z, resol)
         @test reshape(grids.y, 2resol)[1 + 2resol÷2 - 2resol÷4:2resol÷2 + 2resol÷4] == reshape(grids.z, resol)
+
+        @test dV(grids) * 4resol * 2resol * 1resol == 4.0 * 2.0 * 1.0
     end
 end