Merge pull request #21 from KG32/feat/tmx-equivalent-narcotic-depth

Feat/tmx equivalent narcotic depth

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "dive-deco"
-version = "2.0.0"
+version = "2.1.0"
 edition = "2021"
 license = "MIT"
 description = "A dive decompression models library (Buehlmann ZH-L 16C)"

README.md

@@ -25,7 +25,7 @@ The Bühlmann decompression set of parameters is an Haldanian mathematical model
 
 ### Planned features
 
-- extended deco model config [metric/imprial units, water density and more] (currently metric and density assumed to be 1.03kg/l as salt water)
+- extended deco model config [metric/imperial units, water density and more] (currently metric and density assumed to be 1.03kg/l as salt water)
 - travel steps optimization (linear ascent / descent steps using Schreiner equation instead of iterative Haldane equation)
 - BuehlmannModel Default trait implementation
 - other deco algorithms (VPM-B)
@@ -253,6 +253,8 @@ Breathing gas used in the model.
   - he - helium partial pressure
 - `partial_pressures(depth)` - compounded gas's components partial pressures at certain depth
 - `inspired_partial_pressures(depth)` - inspired gas partial pressures in alveoli taking into account alveolar water vapor pressure
+- `maximum_operating_depth(pp_o2_limit)` - maximum operating depth considering o2 partial, with maximum o2 partial pressure as parameter
+- `equivalent_narcotic_depth(depth)` - equivalent depth at which given gas has the same narcotic potential as air. Assumes o2 - n2 1:1 narcotic ratio.
 
 ```rust
 let mix = Gas::new(0.21, 0.);

src/common/deco.rs

@@ -1,10 +1,10 @@
 use crate::{DecoModel, Depth, Gas, Minutes};
-
 use super::{AscentRatePerMinute, DecoModelConfig, DiveState, MbarPressure};
 
-const DEFAULT_ASCENT_RATE: AscentRatePerMinute = 9.;
 // @todo move to model config
+const DEFAULT_ASCENT_RATE: AscentRatePerMinute = 9.;
 const DEFAULT_CEILING_WINDOW: Depth = 3.;
+const DEFAULT_MAX_END_DEPTH: Depth = 30.;
 
 #[derive(Copy, Clone, Debug, PartialEq)]
 enum DecoAction {
@@ -166,7 +166,8 @@ impl Deco {
             if let Some(switch_gas) = next_switch_gas {
                 //switch gas without ascent if within mod of next deco gas
                 let gas_mod = switch_gas.max_operating_depth(1.6);
-                if (switch_gas != current_gas) && (current_depth <= gas_mod) {
+                let gas_end = switch_gas.equivalent_narcotic_depth(current_depth);
+                if (switch_gas != current_gas) && (current_depth <= gas_mod) && (gas_end <= DEFAULT_MAX_END_DEPTH) {
                     return (Some(DecoAction::SwitchGas), Some(switch_gas));
                 }
             }

src/common/gas.rs

@@ -63,8 +63,17 @@ impl Gas {
     }
 
     /// MOD
-    pub fn max_operating_depth(&self, pp_o2: Pressure) -> Depth {
-        10. * ((pp_o2 / self.o2_pp) - 1.)
+    pub fn max_operating_depth(&self, pp_o2_limit: Pressure) -> Depth {
+        10. * ((pp_o2_limit / self.o2_pp) - 1.)
+    }
+
+    /// END
+    pub fn equivalent_narcotic_depth(&self, depth: Depth) -> Depth {
+        let mut end = (depth + 10.) * (1. - self.he_pp) - 10.;
+        if end < 0. {
+           end = 0.;
+        }
+        end
     }
 
     // TODO standard nitrox (bottom and deco) and trimix gasses
@@ -76,6 +85,8 @@ impl Gas {
 
 #[cfg(test)]
 mod tests {
+    use std::f64::INFINITY;
+
     use super::*;
 
     #[test]
@@ -136,10 +147,32 @@ mod tests {
 
     #[test]
     fn test_mod() {
-        let air = Gas::new(0.21, 0.);
-        let ean_50 = Gas::new(0.50, 0.);
-        assert_eq!(air.max_operating_depth(1.4), 56.66666666666666);
-        assert_eq!(ean_50.max_operating_depth(1.6), 22.);
+        // o2, he, max_ppo2, MOD
+        let test_cases = [
+            (0.21, 0., 1.4, 56.66666666666666),
+            (0.50, 0., 1.6, 22.),
+            (0.21, 0.35, 1.4, 56.66666666666666),
+            (0., 0., 1.4, INFINITY),
+        ];
+        for (pp_o2, pe_he, max_pp_o2, expected_mod) in test_cases {
+            let gas = Gas::new(pp_o2, pe_he);
+            let calculated_mod = gas.max_operating_depth(max_pp_o2);
+            assert_eq!(calculated_mod, expected_mod);
+        }
+    }
 
+    #[test]
+    fn test_end() {
+        // depth, o2, he, END
+        let test_cases = [
+            (60., 0.21, 0.40, 32.),
+            (0., 0.21, 0.40, 0.),
+            (40., 0.21, 0., 40.),
+        ];
+        for (depth, o2_pp, he_pp, expected_end) in test_cases {
+            let tmx = Gas::new(o2_pp, he_pp);
+            let calculated_end = tmx.equivalent_narcotic_depth(depth);
+            assert_eq!(calculated_end, expected_end);
+        }
     }
 }