From 9fcd733232b6f209519d2eadc83ed4cbd3376e0d Mon Sep 17 00:00:00 2001
From: Elizabeth Hunt <elizabeth.hunt@simponic.xyz>
Date: Thu, 7 Sep 2023 12:19:32 -0600
Subject: common lisp!

---
 cl/src/approx/derivative.lisp | 8 ++++++++
 1 file changed, 8 insertions(+)
 create mode 100644 cl/src/approx/derivative.lisp

(limited to 'cl/src/approx/derivative.lisp')

diff --git a/cl/src/approx/derivative.lisp b/cl/src/approx/derivative.lisp
new file mode 100644
index 0000000..280463f
--- /dev/null
+++ b/cl/src/approx/derivative.lisp
@@ -0,0 +1,8 @@
+(in-package :lizfcm.approx)
+
+(defun derivative-at (f x &optional (delta 0.01))
+  (let* ((x2 (+ x delta))
+         (x1 (- x delta))
+         (y2 (apply f (list x2)))
+         (y1 (apply f (list x1))))
+    (/ (- y2 y1) (- x2 x1))))
-- 
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