Added volume.

README.md

@@ -13,10 +13,8 @@ I'm using this code to explore human survivability given global warming. The fol
 3. [Extreme Heat](https://www.journeyman.cc/blog/posts-output/2026-07-31-Extreme-Heat/)
 4. [Analysis of 2026 heatwaves UK](https://www.journeyman.cc/blog/posts-output/2026-08-04-Analysis-of-2026-heatwaves-UK/)
 
-
 ## Status
 
-
 Alpha-quality code. It more or less works but it isn't at all polished.
 
 ## General architecture
@@ -26,16 +24,18 @@ Alpha-quality code. It more or less works but it isn't at all polished.
 The 'packet', in the terminology of this library, is a map which has bindings
 for some of the following keywords:
 
-1. `:absolute-humidity`
+1. `:absolute-humidity` *grammes per metre<sup>3</sup>.*
 2. `:actual-vapour-pressure` *not yet implemented*
 1. `:dew-point` *not yet implemented*
 2. `:pressure-pascals` 
 3. `:pressure-millibars` 
-4. `:saturation-vapour-pressure`
-5. `:relative-humidity`
-6. `:temperature` *assumed to be celsius*
+4. `:saturation-vapour-pressure` *Pascals*
+5. `:relative-humidity` *percentage, 0...100.*
+6. `:temperature` *assumed to be &deg; Celsius*
 7. `:temperature-celsius` 
 8. `:temperature-kelvin` 
+9. `:volume` *in metres<sup>3</sup>, relative to 1 at standard temperature and pressure.*
+10. `:wet-bulb-temperature` *in &deg; Celsius.*
 
 These keywords represent variables in the pressure equations, and they are all
 to a degree inter-related; so if you have (or can assume) some of them, you can

src/humidity/actual_vp.clj

@@ -1,4 +1,6 @@
-(ns humidity.actual-vp)
+(ns ^{:author "simon"
+  :authority "https://www.weather.gov/media/epz/wxcalc/vaporPressure.pdf"
+  :doc "Compute actual vapour pressure."} humidity.actual-vp)
 
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

src/humidity/core.clj

@@ -6,6 +6,7 @@
             [humidity.relative :refer [rel-humidity]]
             [humidity.saturation-vp :refer [saturation-vp]]
             [humidity.utils :refer [?assoc]]
+            [humidity.volume :refer [volume-fn]]
             [humidity.wet-bulb :as wb]))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
@@ -33,7 +34,8 @@
   "Resolve humidity equations given the data in this packet."
   [& {:keys [absolute-humidity pressure-pascals pressure-millibars
              relative-humidity saturation-vapour-pressure temperature
-             temperature-celsius temperature-kelvin wet-bulb-temperature] :as packet}]
+             temperature-celsius temperature-kelvin volume
+             wet-bulb-temperature] :as packet}]
   (println packet)
   (if temperature (resolve-humidity
                    (assoc (dissoc packet :temperature)
@@ -46,7 +48,8 @@
                                     (* pressure-millibars 100) Pa))
               :pressure-millibars (when-not pressure-millibars
                                     (if pressure-pascals
-                                      (/ pressure-pascals 100) (/ Pa 100)))
+                                     (float (/ pressure-pascals 100))
+                                     (float (/ Pa 100))))
               :relative-humidity (when-not relative-humidity
                                    (rel-humidity packet))
               :saturation-vapour-pressure (when-not saturation-vapour-pressure
@@ -59,6 +62,7 @@
                                    (and temperature-celsius
                                         (not temperature-kelvin))
                                     (+ temperature-celsius celsius-offset))
+              :volume (when-not volume (volume-fn packet))
               :wet-bulb-temperature (when-not wet-bulb-temperature
                                       (wb/wet-bulb-temperature packet)))))
 

src/humidity/volume.clj

@@ -0,0 +1,22 @@
+(ns ^{:author "simon"
+      :authority "https://en.wikipedia.org/wiki/Gas_laws"
+      :doc "In computing the relative humidity of air after it has warmed, I need
+  to account for the change in volume. By Charles' Law, given stable
+  pressure, volume is proportinal to absolute temperature (i.e. V=Tk, where K
+  is a constant). However, the sources I have read do not give that constant,
+  for air. But seeing what I'm interested in is that amount of air which is
+  contained in a cubic metre at standard temperature and pressure, then *I
+  think* I can just take (temperature-kelvin/celsius-offset) as the temperature
+  component.
+
+  Gay-Lussac's law says pretty much the same for pressure, so again *I think* I
+  can take (pressure-pascals/Pa) as the pressure component."} humidity.volume
+  (:require [humidity.constants :refer [celsius-offset Pa]]))
+
+(defn volume-fn
+  "Compute the volume, in m<sup>3</sup> of a quantity of air which would be
+  1m<sup>3</sup> at standard temperature and pressure, given temperature in
+  &deg; Kelvin and pressure in Pascals."
+  [& {:keys [temperature-kelvin pressure-pascals]}]
+  (when (and temperature-kelvin pressure-pascals)
+    (* (/ temperature-kelvin celsius-offset) (/ pressure-pascals Pa))))

test/humidity/core_test.clj

@@ -29,10 +29,11 @@
   (let [expected {:relative-humidity 100,
                   :temperature-celsius 35,
                   :pressure-pascals 101325,
-    :pressure-millibars 4053/4,
+                  :pressure-millibars 1013.25,
                   :saturation-vapour-pressure 5622.488734516426,
                   :temperature-kelvin 308.15,
-    :absolute-humidity 3953.618101887827}
+                  :absolute-humidity 3953.618101887827,
+                  :volume 1.1281347245103424}
         packet {:relative-humidity 100 :temperature-celsius 35}
         actual (resolution packet)]
     (is (= actual expected))))

test/humidity/volume_test.clj

@@ -0,0 +1,41 @@
+(ns humidity.volume-test
+  (:require [clojure.test :refer [deftest is testing]]
+            [humidity.constants :refer [celsius-offset Pa]]
+            [humidity.volume :refer [volume-fn]]))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;;
+;;; Copyright (C) 2026 Simon Brooke
+;;;
+;;; This program is free software; you can redistribute it and/or
+;;; modify it under the terms of the GNU General Public License
+;;; as published by the Free Software Foundation; either version 2
+;;; of the License, or (at your option) any later version.
+;;;
+;;; This program is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with this program; if not, write to the Free Software
+;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
+;;; USA.
+;;;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(deftest relative-humidity-test
+  (testing "definitional"
+    (let [min-expected 0.99
+          max-expected 1.01
+          actual (volume-fn :pressure-pascals Pa :temperature-kelvin celsius-offset)]
+      (is (< min-expected actual max-expected))))
+  (testing "Example from metoffice 26th May data."
+    (let [min-expected 1.14
+          max-expected 1.15
+          actual (volume-fn :pressure-pascals 102600 :temperature-kelvin (+ 35.1 celsius-offset))]
+      (is (< min-expected actual max-expected)))
+    (testing "Missing data returns nil"
+      (let [expected nil
+            actual (volume-fn :pressure-pascals 102600 :temperature-celsius 35.1)]
+        (is (= actual expected))))))