Revert back.

src/math.rs

@@ -1,30 +1,20 @@
-use std::f64;
-
-fn erfc(x: f64) -> f64 {
-    let z = x.abs();
-    let t = 1.0 / (1.0 + z / 2.0);
-    let r = t
-        * (-z * z - 1.26551223
-            + t * (1.00002368
-                + t * (0.37409196
-                    + t * (0.09678418
-                        + t * (-0.18628806
-                            + t * (0.27886807
-                                + t * (-1.13520398
-                                    + t * (1.48851587 + t * (-0.82215223 + t * 0.17087277)))))))))
-            .exp();
-
-    if x < 0.0 {
-        2.0 - r
-    } else {
-        r
-    }
-}
+use statrs::distribution::{Normal, Univariate, Continuous};
 
 pub fn cdf(x: f64) -> f64 {
-    0.5 * erfc(-x / 2.0f64.sqrt())
+    Normal::new(0.0, 1.0).unwrap().cdf(x)
 }
 
 pub fn pdf(x: f64) -> f64 {
-    1.0 / (2.0 * f64::consts::PI).sqrt() * (-((x / 1.0).powi(2) / 2.0)).exp()
+    Normal::new(0.0, 1.0).unwrap().pdf(x)
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_cdf() {
+        assert_eq!(cdf(0.5), 0.6914624612740131);
+    }
 }