Add thermo polynomial calculations

src/properties/thermo_fit.rs

@@ -20,3 +20,93 @@ pub struct SpeciesElement {
     pub element: String,
     pub count: f64,
 }
+
+impl ThermoPolynomial {
+    /// Calculate using eq 4.9 from reference paper
+    /// NOTE: This is normalized and unitless
+    pub fn cp_over_r(self, temp: f64) -> f64 {
+        let inv_temp = 1.0 / temp;
+        self.a[0] * inv_temp * inv_temp
+            + self.a[1] * inv_temp
+            + self.a[2]
+            + self.a[3] * temp
+            + self.a[4] * temp * temp
+            + self.a[5] * temp * temp * temp
+            + self.a[6] * temp * temp * temp * temp
+    }
+    /// Calculate using eq 4.10 from reference paper
+    /// NOTE: This is normalized and unitless
+    pub fn h_over_rt(self, temp: f64) -> f64 {
+        let inv_temp = 1.0 / temp;
+        -self.a[0] * inv_temp * inv_temp
+            + self.a[1] * inv_temp * inv_temp.ln()
+            + self.a[2]
+            + self.a[3] * temp / 2.0
+            + self.a[4] * temp * temp / 3.0
+            + self.a[5] * temp * temp * temp / 4.0
+            + self.a[6] * temp * temp * temp * temp / 5.0
+            + self.a[7] * inv_temp
+    }
+    /// Calculate using eq 4.11 from reference paper
+    /// NOTE: This is normalized and unitless
+    pub fn s_over_r(self, temp: f64) -> f64 {
+        let inv_temp = 1.0 / temp;
+        -self.a[0] * inv_temp * inv_temp - self.a[1] * inv_temp
+            + self.a[2] * temp.ln()
+            + self.a[3] * temp
+            + self.a[4] * temp * temp / 2.0
+            + self.a[5] * temp * temp * temp / 3.0
+            + self.a[6] * temp * temp * temp * temp / 4.0
+            + self.a[8]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::assert_delta;
+    use super::ThermoPolynomial;
+
+    fn poly(a: Vec<f64>) -> ThermoPolynomial {
+        ThermoPolynomial { a, temp_range: (0.0, 0.0) }
+    }
+
+    #[test]
+    fn test_cp_over_r() {
+        // At T=1: a[0]/T^2 + a[1]/T + a[2] + a[3]*T + a[4]*T^2 + a[5]*T^3 + a[6]*T^4
+        // = 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28
+        let result = poly(vec![1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0]).cp_over_r(1.0);
+        assert_delta!(result, 28.0, 1e-10);
+
+        // At T=2: 4/4 + 2/2 + 1 + 2*2 + 1*4 + 1*8 + 1*16 = 35
+        let result = poly(vec![4.0, 2.0, 1.0, 2.0, 1.0, 1.0, 1.0]).cp_over_r(2.0);
+        assert_delta!(result, 35.0, 1e-10);
+    }
+
+    #[test]
+    fn test_h_over_rt() {
+        // At T=1: ln(1/T)=0, so the a[1] term vanishes
+        // -a[0] + 0 + a[2] + a[3]/2 + a[4]/3 + a[5]/4 + a[6]/5 + a[7]
+        // = -1 + 0 + 3 + 12/2 + 9/3 + 8/4 + 5/5 + 8 = -1+3+6+3+2+1+8 = 22
+        let result = poly(vec![1.0, 2.0, 3.0, 12.0, 9.0, 8.0, 5.0, 8.0]).h_over_rt(1.0);
+        assert_delta!(result, 22.0, 1e-10);
+
+        // At T=2: a[1]=0 so log term vanishes; a[4..6]=0 to avoid fractions
+        // -4/4 + 0 + 3 + 4*2/2 + 0 + 0 + 0 + 2/2 = -1+3+4+1 = 7
+        let result = poly(vec![4.0, 0.0, 3.0, 4.0, 0.0, 0.0, 0.0, 2.0]).h_over_rt(2.0);
+        assert_delta!(result, 7.0, 1e-10);
+    }
+
+    #[test]
+    fn test_s_over_r() {
+        // At T=1: ln(T)=0, so a[2] term vanishes
+        // -a[0] - a[1] + 0 + a[3] + a[4]/2 + a[5]/3 + a[6]/4 + a[8]
+        // = -1-2+0+4+6/2+12/3+8/4+5 = -1-2+4+3+4+2+5 = 15
+        let result = poly(vec![1.0, 2.0, 3.0, 4.0, 6.0, 12.0, 8.0, 0.0, 5.0]).s_over_r(1.0);
+        assert_delta!(result, 15.0, 1e-10);
+
+        // At T=2: a[2]=0 so log term vanishes; a[5..6]=0 to avoid fractions
+        // -4/4 - 2/2 + 0 + 2*2 + 2*4/2 + 0 + 0 + 3 = -1-1+4+4+3 = 9
+        let result = poly(vec![4.0, 2.0, 0.0, 2.0, 2.0, 0.0, 0.0, 0.0, 3.0]).s_over_r(2.0);
+        assert_delta!(result, 9.0, 1e-10);
+    }
+}