feat: simplifies LR API

src/linalg/ndarray_bindings.rs

@@ -1,9 +1,20 @@
 use std::ops::Range;
 use crate::linalg::{Matrix};
-use ndarray::{Array, ArrayBase, OwnedRepr, Ix2, Axis, stack, s};
+use ndarray::{Array, ArrayBase, OwnedRepr, Ix2, Ix1, Axis, stack, s};
 
 impl Matrix for ArrayBase<OwnedRepr<f64>, Ix2>
 {
+    type RowVector = ArrayBase<OwnedRepr<f64>, Ix1>;
+
+    fn from_row_vector(vec: Self::RowVector) -> Self{
+        let vec_size = vec.len();
+        vec.into_shape((1, vec_size)).unwrap()
+    }
+
+    fn to_row_vector(self) -> Self::RowVector{
+        let vec_size = self.nrows() * self.ncols();
+        self.into_shape(vec_size).unwrap()
+    }
 
     fn from_array(nrows: usize, ncols: usize, values: &[f64]) -> Self {
         Array::from_shape_vec((nrows, ncols), values.to_vec()).unwrap()     
@@ -248,7 +259,16 @@ impl Matrix for ArrayBase<OwnedRepr<f64>, Ix2>
 #[cfg(test)]
 mod tests {    
     use super::*; 
-    use ndarray::{arr2, Array2};
+    use ndarray::{arr1, arr2, Array2};
+
+    #[test]
+    fn from_to_row_vec() { 
+
+        let vec = arr1(&[ 1.,  2.,  3.]);
+        assert_eq!(Array2::from_row_vector(vec.clone()), arr2(&[[1., 2., 3.]]));
+        assert_eq!(Array2::from_row_vector(vec.clone()).to_row_vector(), arr1(&[1., 2., 3.]));
+
+    }
 
     #[test]
     fn add_mut() {