Add examples for covariance and correlation

examples/correlation.rs

@@ -0,0 +1,45 @@
+use rustframe::compute::stats::{covariance, covariance_matrix, pearson};
+use rustframe::matrix::{Axis, Matrix};
+
+/// Demonstrates covariance and correlation utilities.
+fn main() {
+    pairwise_cov();
+    println!("\n-----\n");
+    matrix_cov();
+}
+
+fn pairwise_cov() {
+    println!("Covariance & Pearson r\n----------------------");
+    let x = Matrix::from_vec(vec![1.0, 2.0, 3.0, 4.0], 2, 2);
+    let y = Matrix::from_vec(vec![1.0, 2.0, 3.0, 5.0], 2, 2);
+    println!("covariance : {:.2}", covariance(&x, &y));
+    println!("pearson r  : {:.3}", pearson(&x, &y));
+}
+
+fn matrix_cov() {
+    println!("Covariance matrix\n-----------------");
+    let data = Matrix::from_rows_vec(vec![1.0, 2.0, 3.0, 4.0], 2, 2);
+    let cov = covariance_matrix(&data, Axis::Col);
+    println!("cov matrix : {:?}", cov.data());
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    const EPS: f64 = 1e-8;
+
+    #[test]
+    fn test_pairwise_cov() {
+        let x = Matrix::from_vec(vec![1.0, 2.0, 3.0, 4.0], 2, 2);
+        let y = Matrix::from_vec(vec![1.0, 2.0, 3.0, 5.0], 2, 2);
+        assert!((covariance(&x, &y) - 1.625).abs() < EPS);
+        assert!((pearson(&x, &y) - 0.9827076298239908).abs() < 1e-5,);
+    }
+
+    #[test]
+    fn test_matrix_cov() {
+        let data = Matrix::from_rows_vec(vec![1.0, 2.0, 3.0, 4.0], 2, 2);
+        let cov = covariance_matrix(&data, Axis::Col);
+        assert_eq!(cov.data(), &[2.0, 2.0, 2.0, 2.0]);
+    }
+}