From 4f2afb1ca7063206411475bce89669238e41cb2b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juan=20Manuel=20Tom=C3=A1s?= <jtomas1815@gmail.com>
Date: Thu, 14 Jan 2021 07:03:01 -0300
Subject: Implement derivative of polynomials

---
 src/poly.rs | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/poly.rs b/src/poly.rs
index 90b7b78..cb84d64 100644
--- a/src/poly.rs
+++ b/src/poly.rs
@@ -117,10 +117,24 @@ 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]);
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