diff --git a/src/classification/logistic_regression.rs b/src/classification/logistic_regression.rs
index faacb2d..919a637 100644
--- a/src/classification/logistic_regression.rs
+++ b/src/classification/logistic_regression.rs
@@ -139,8 +139,7 @@ impl<M: Matrix> LogisticRegression<M> {
         let mut yi: Vec<usize> = vec![0; y_nrows];
 
         for i in 0..y_nrows {
-            let yc = y_m.get(0, i); 
-            let j = classes.iter().position(|c| yc == *c).unwrap();            
+            let yc = y_m.get(0, i);             
             yi[i] = classes.iter().position(|c| yc == *c).unwrap();
         }
 
@@ -244,7 +243,7 @@ impl<M: Matrix> LogisticRegression<M> {
 mod tests {    
     use super::*; 
     use crate::linalg::naive::dense_matrix::*;       
-    use ndarray::{arr1, arr2, Array};
+    use ndarray::{arr1, arr2};
 
     #[test]
     fn multiclass_objective_f() { 
diff --git a/src/error.rs b/src/error.rs
deleted file mode 100644
index 42f7632..0000000
--- a/src/error.rs
+++ /dev/null
@@ -1,12 +0,0 @@
-use std::fmt;
-
-#[derive(Debug)]
-pub struct IllegalArgumentError {
-    pub message: String,
-}
-
-impl fmt::Display for IllegalArgumentError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {        
-        write!(f, "{}", self.message)
-    }
-}
\ No newline at end of file
diff --git a/src/lib.rs b/src/lib.rs
index 63eeea7..a340717 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -4,7 +4,6 @@ pub mod cluster;
 pub mod decomposition;
 pub mod linalg;
 pub mod math;
-pub mod error;
 pub mod algorithm;
 pub mod common;
 pub mod optimization;
\ No newline at end of file
diff --git a/src/linalg/evd.rs b/src/linalg/evd.rs
index f4467f5..d7b993a 100644
--- a/src/linalg/evd.rs
+++ b/src/linalg/evd.rs
@@ -1,3 +1,5 @@
+#![allow(non_snake_case)]
+
 use num::complex::Complex;
 use crate::linalg::BaseMatrix;
 
diff --git a/src/linalg/mod.rs b/src/linalg/mod.rs
index 3565815..0f1a5f1 100644
--- a/src/linalg/mod.rs
+++ b/src/linalg/mod.rs
@@ -122,9 +122,7 @@ pub trait BaseMatrix: Clone + Debug {
         r
     }
 
-    fn transpose(&self) -> Self;
-
-    fn generate_positive_definite(nrows: usize, ncols: usize) -> Self;
+    fn transpose(&self) -> Self;    
 
     fn rand(nrows: usize, ncols: usize) -> Self;
 
diff --git a/src/linalg/naive/dense_matrix.rs b/src/linalg/naive/dense_matrix.rs
index ace051d..ba50298 100644
--- a/src/linalg/naive/dense_matrix.rs
+++ b/src/linalg/naive/dense_matrix.rs
@@ -366,12 +366,7 @@ impl BaseMatrix for DenseMatrix {
 
     fn sub_element_mut(&mut self, row: usize, col: usize, x: f64) {
         self.values[col*self.nrows + row] -= x;
-    }  
-
-    fn generate_positive_definite(nrows: usize, ncols: usize) -> Self {
-        let m = DenseMatrix::rand(nrows, ncols);
-        m.dot(&m.transpose())
-    }
+    }    
 
     fn transpose(&self) -> Self {
         let mut m = DenseMatrix {
@@ -723,11 +718,6 @@ mod tests {
         }
     }
 
-    #[test]
-    fn generate_positive_definite() {
-        let m = DenseMatrix::generate_positive_definite(3, 3);        
-    }
-
     #[test]
     fn reshape() {
         let m_orig = DenseMatrix::vector_from_array(&[1., 2., 3., 4., 5., 6.]);
diff --git a/src/linalg/ndarray_bindings.rs b/src/linalg/ndarray_bindings.rs
index 111a2f3..fe883e5 100644
--- a/src/linalg/ndarray_bindings.rs
+++ b/src/linalg/ndarray_bindings.rs
@@ -5,6 +5,7 @@ use crate::linalg::svd::SVDDecomposableMatrix;
 use crate::linalg::evd::EVDDecomposableMatrix;
 use crate::linalg::qr::QRDecomposableMatrix;
 use ndarray::{Array, ArrayBase, OwnedRepr, Ix2, Ix1, Axis, stack, s};
+use rand::prelude::*;
 
 impl BaseMatrix for ArrayBase<OwnedRepr<f64>, Ix2>
 {
@@ -81,7 +82,7 @@ impl BaseMatrix for ArrayBase<OwnedRepr<f64>, Ix2>
     }
 
     fn approximate_eq(&self, other: &Self, error: f64) -> bool {
-        false
+        (self - other).iter().all(|v| v.abs() <= error)
     }
 
     fn add_mut(&mut self, other: &Self) -> &Self {
@@ -128,12 +129,12 @@ impl BaseMatrix for ArrayBase<OwnedRepr<f64>, Ix2>
         self.clone().reversed_axes()
     }
 
-    fn generate_positive_definite(nrows: usize, ncols: usize) -> Self{
-        panic!("generate_positive_definite method is not implemented for ndarray");
-    }
-
     fn rand(nrows: usize, ncols: usize) -> Self{
-        panic!("rand method is not implemented for ndarray");
+        let mut rng = rand::thread_rng();
+        let values: Vec<f64> = (0..nrows*ncols).map(|_| {
+            rng.gen()
+        }).collect();
+        Array::from_shape_vec((nrows, ncols), values).unwrap()
     }
 
     fn norm2(&self) -> f64{
@@ -600,4 +601,26 @@ mod tests {
         let res: Array2<f64> = BaseMatrix::eye(3);
         assert_eq!(res, a);
     }
+
+    #[test]
+    fn rand() {
+        let m: Array2<f64> = BaseMatrix::rand(3, 3);
+        for c in 0..3 {
+            for r in 0..3 {
+                assert!(m[[r, c]] != 0f64);
+            }
+        }
+    }
+
+    #[test]
+    fn approximate_eq() {
+        let a = arr2(&[[1., 2., 3.],
+            [4., 5., 6.], 
+            [7., 8., 9.]]);
+        let noise = arr2(&[[1e-5, 2e-5, 3e-5],
+            [4e-5, 5e-5, 6e-5], 
+            [7e-5, 8e-5, 9e-5]]);        
+        assert!(a.approximate_eq(&(&noise + &a), 1e-4));
+        assert!(!a.approximate_eq(&(&noise + &a), 1e-5));
+    }
 }
\ No newline at end of file
diff --git a/src/linalg/qr.rs b/src/linalg/qr.rs
index e99be6a..bffeec2 100644
--- a/src/linalg/qr.rs
+++ b/src/linalg/qr.rs
@@ -1,3 +1,5 @@
+#![allow(non_snake_case)]
+
 use crate::linalg::BaseMatrix;
 
 #[derive(Debug, Clone)]
diff --git a/src/linalg/svd.rs b/src/linalg/svd.rs
index 0f1ff21..665f394 100644
--- a/src/linalg/svd.rs
+++ b/src/linalg/svd.rs
@@ -1,3 +1,5 @@
+#![allow(non_snake_case)]
+
 use crate::linalg::BaseMatrix;
 
 #[derive(Debug, Clone)]
@@ -504,7 +506,7 @@ mod tests {
     #[test]
     fn solve() { 
 
-            let mut a = DenseMatrix::from_array(&[&[0.9, 0.4, 0.7], &[0.4, 0.5, 0.3], &[0.7, 0.3, 0.8]]);
+            let a = DenseMatrix::from_array(&[&[0.9, 0.4, 0.7], &[0.4, 0.5, 0.3], &[0.7, 0.3, 0.8]]);
             let b = DenseMatrix::from_array(&[&[0.5, 0.2],&[0.5, 0.8], &[0.5, 0.3]]);
             let expected_w = DenseMatrix::from_array(&[
                 &[-0.20, -1.28],
diff --git a/src/math/distance/euclidian.rs b/src/math/distance/euclidian.rs
index a449f74..2d5b88a 100644
--- a/src/math/distance/euclidian.rs
+++ b/src/math/distance/euclidian.rs
@@ -21,7 +21,7 @@ mod tests {
     use super::*;    
 
     #[test]
-    fn measure_simple_euclidian_distance() {
+    fn squared_distance() {
         let a = vec![1., 2., 3.];
         let b = vec![4., 5., 6.];             
         
diff --git a/src/math/mod.rs b/src/math/mod.rs
index 0946afb..f091f7a 100644
--- a/src/math/mod.rs
+++ b/src/math/mod.rs
@@ -9,9 +9,7 @@ pub trait NumericExt {
 
 impl NumericExt for f64 {
 
-    fn ln_1pe(&self) -> f64{
-        let y = 0.;
-
+    fn ln_1pe(&self) -> f64{        
         if *self > 15. {
             return *self;
         } else {
diff --git a/src/optimization/first_order/lbfgs.rs b/src/optimization/first_order/lbfgs.rs
index cf8aa76..d1bd8f9 100644
--- a/src/optimization/first_order/lbfgs.rs
+++ b/src/optimization/first_order/lbfgs.rs
@@ -154,7 +154,7 @@ impl LBFGS {
         g_converged || x_converged || state.counter_f_tol > self.successive_f_tol
     }
 
-    fn update_hessian<'a, X: Matrix>(&self, df: &'a DF<X>, state: &mut LBFGSState<X>) {                      
+    fn update_hessian<'a, X: Matrix>(&self, _: &'a DF<X>, state: &mut LBFGSState<X>) {                      
         state.dg = state.x_df.sub(&state.x_df_prev);            
         let rho_iteration = 1. / state.dx.vector_dot(&state.dg);
         if !rho_iteration.is_infinite() {
diff --git a/src/optimization/mod.rs b/src/optimization/mod.rs
index 157a6ca..8d97662 100644
--- a/src/optimization/mod.rs
+++ b/src/optimization/mod.rs
@@ -1,10 +1,8 @@
 pub mod first_order;
 pub mod line_search;
 
-use crate::linalg::Matrix;
-
-pub type F<'a, X: Matrix> = dyn for<'b> Fn(&'b X) -> f64 + 'a;
-pub type DF<'a, X: Matrix> = dyn for<'b> Fn(&'b mut X, &'b X) + 'a;
+pub type F<'a, X> = dyn for<'b> Fn(&'b X) -> f64 + 'a;
+pub type DF<'a, X> = dyn for<'b> Fn(&'b mut X, &'b X) + 'a;
 
 #[derive(Debug, PartialEq)]
 pub enum FunctionOrder {
diff --git a/src/regression/linear_regression.rs b/src/regression/linear_regression.rs
index db522b3..adf2d38 100644
--- a/src/regression/linear_regression.rs
+++ b/src/regression/linear_regression.rs
@@ -1,5 +1,4 @@
 use crate::linalg::Matrix;
-use crate::regression::Regression;
 use std::fmt::Debug;
 
 #[derive(Debug)]
@@ -27,7 +26,7 @@ impl<M: Matrix> LinearRegression<M> {
             panic!("Number of rows of X doesn't match number of rows of Y");
         }
                 
-        let mut a = x.v_stack(&M::ones(x_nrows, 1));
+        let a = x.v_stack(&M::ones(x_nrows, 1));
 
         let w = match solver {
             LinearRegressionSolver::QR => a.qr_solve_mut(b),
@@ -43,16 +42,11 @@ impl<M: Matrix> LinearRegression<M> {
         }
     }
 
-}
-
-impl<M: Matrix> Regression<M> for LinearRegression<M> {
-
-
-    fn predict(&self, x: &M) -> M {
+    pub fn predict(&self, x: &M) -> M::RowVector {
         let (nrows, _) = x.shape();
         let mut y_hat = x.dot(&self.coefficients);
         y_hat.add_mut(&M::fill(nrows, 1, self.intercept));
-        y_hat.transpose()
+        y_hat.transpose().to_row_vector()
     }
 
 }
@@ -85,9 +79,9 @@ mod tests {
         
             let y = DenseMatrix::from_array(&[&[83.0,  88.5,  88.2,  89.5,  96.2,  98.1,  99.0, 100.0, 101.2, 104.6, 108.4, 110.8, 112.6, 114.2, 115.7, 116.9]]);            
 
-            let y_hat_qr = LinearRegression::fit(&x, &y, LinearRegressionSolver::QR).predict(&x);                        
+            let y_hat_qr = DenseMatrix::from_row_vector(LinearRegression::fit(&x, &y, LinearRegressionSolver::QR).predict(&x));                        
 
-            let y_hat_svd = LinearRegression::fit(&x, &y, LinearRegressionSolver::SVD).predict(&x);
+            let y_hat_svd = DenseMatrix::from_row_vector(LinearRegression::fit(&x, &y, LinearRegressionSolver::SVD).predict(&x));
 
             assert!(y.approximate_eq(&y_hat_qr, 5.));
             assert!(y.approximate_eq(&y_hat_svd, 5.));
diff --git a/src/regression/mod.rs b/src/regression/mod.rs
index c4bc5a4..d765146 100644
--- a/src/regression/mod.rs
+++ b/src/regression/mod.rs
@@ -1,9 +1 @@
-pub mod linear_regression;
-
-use crate::linalg::Matrix;
-
-pub trait Regression<M: Matrix> {    
-
-    fn predict(&self, x: &M) -> M;
-
-}
\ No newline at end of file
+pub mod linear_regression;
\ No newline at end of file