Implement derivative of polynomials

1 files changed, 14 insertions, 0 deletions

diff --git a/src/poly.rs b/src/poly.rs
index 90b7b78..cb84d64 100644
--- a/src/poly.rs
+++ b/src/poly.rs
@@ -117,11 +117,25 @@ pub fn gcd(a: &Poly, b: &Poly) -> Poly {
     }
 }
 
+pub fn derivative(p: &Poly) -> Poly {
+    let mut v = vec![0.0; p.degree()];
+    for i in 0..v.len() {
+        v[i] = p.data[i + 1] * (i + 1) as Number;
+    }
+    Poly::new(v)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
     #[test]
+    fn derivative_test() {
+        let p = Poly::new(vec![1.0, 2.0, 3.0, 4.0, 5.0]);
+        assert_eq!(derivative(&p), Poly::new(vec![2.0, 6.0, 12.0, 20.0]));
+    }
+
+    #[test]
     fn div_equal() {
         let a = Poly::new(vec![6.0, 7.0, 1.0]);
         let b = Poly::new(vec![-6.0, -5.0, 1.0]);