fix bug, add test in tests folder

src/base/mod.rs

@@ -64,5 +64,3 @@ pub use self::matrix_view::*;
 pub use self::storage::*;
 #[cfg(any(feature = "std", feature = "alloc"))]
 pub use self::vec_storage::*;
-
-mod variance_test;

src/base/statistics.rs

@@ -335,16 +335,12 @@ impl<T: Scalar, R: Dim, C: Dim, S: RawStorage<T, R, C>> Matrix<T, R, C, S> {
         if self.is_empty() {
             T::zero()
         } else {
-            // cannot use sum since `T` is not `Sum` by trait bounds
-            let sum_of_elements = self.iter().cloned().fold(T::zero(), |a, b| a + b);
-            let n_elements = crate::convert::<_, T>(self.len() as f64);
-            let mean = sum_of_elements / n_elements.clone();
+            let n_elements: T = crate::convert(self.len() as f64);
+            let mean = self.mean();
 
-            let variance = self.iter().cloned().fold(T::zero(), |acc, x| {
+            self.iter().cloned().fold(T::zero(), |acc, x| {
                 acc + (x.clone() - mean.clone()) * (x.clone() - mean.clone())
-            }) / n_elements;
-
-            variance
+            }) / n_elements
         }
     }
 

tests/core/mod.rs

@@ -11,6 +11,7 @@ mod reshape;
 #[cfg(feature = "rkyv-serialize-no-std")]
 mod rkyv;
 mod serde;
+mod variance;
 
 #[cfg(feature = "compare")]
 mod matrixcompare;

tests/core/variance.rs

@@ -1,10 +1,10 @@
-#[cfg(test)]
-use crate::DVector;
+use nalgebra::DVector;
 #[test]
 fn test_variance_new() {
     let long_repeating_vector = DVector::repeat(10_000, 100000000.0);
     assert_eq!(long_repeating_vector.variance(), 0.0);
 
     let short_vec = DVector::from_vec(vec![1., 2., 3.]);
-    assert_eq!(short_vec.variance(), 2.0 / 3.0)
+
+    assert_eq!(short_vec.variance(), 2.0 / 3.0);
 }