Simplify vector operations in natural_cubic.rs

Changed the way vectors are handled in the natural_cubic.rs file resulting in more readable and efficient code. The new implementation reduces the use of separate operations and duplicates, and avoids the unnecessary creation of new containers for the intermediate results.

crates/qlab-math/src/interpolation/spline/natural_cubic.rs

@@ -1,7 +1,7 @@
 use crate::interpolation::spline::Value;
 use crate::interpolation::{find_index_at_left_boundary, Interpolator, Point2DWithSlope};
 use crate::linear_algebra::tridiagonal_matrix::TridiagonalMatrix;
-use nalgebra::{DVector, Dim, Dyn, VecStorage, U1};
+use nalgebra::DVector;
 use qlab_error::InterpolationError;
 
 #[derive(Default)]
@@ -72,11 +72,7 @@ impl<V: Value> Interpolator<NaturalCubic<V>, V> for NaturalCubic<V> {
         for raw_point in raw_points.iter().take(raw_points.len() - 1).skip(1) {
             y.push(raw_point.1);
         }
-        let rhs = VecStorage::new(Dyn::from_usize(raw_points.len() - 2), U1, (c * y).unwrap());
-        let mut rhs = DVector::from_data(rhs);
-        let m = VecStorage::new(Dyn::from_usize(raw_points.len() - 2), U1, m);
-        let m = DVector::from_data(m);
-        rhs += m;
+        let rhs = DVector::from((c * y).unwrap()) + DVector::from(m);
         let y2 = b.solve(rhs.as_slice());
         let mut derivatives = Vec::with_capacity(raw_points.len());
         derivatives.push(V::zero());
@@ -86,7 +82,7 @@ impl<V: Value> Interpolator<NaturalCubic<V>, V> for NaturalCubic<V> {
         derivatives.push(V::zero());
 
         let mut temp = raw_points[0].0;
-        let mut points = Vec::new();
+        let mut points = Vec::with_capacity(raw_points.len());
         for (&(x, y), dydx) in raw_points.iter().zip(derivatives) {
             let point = Point2DWithSlope::new(x, y, dydx);
             if point.coordinate.x < temp {