3 files changed, 25 insertions, 0 deletions
diff --git a/src/approx/derivative.lisp b/src/approx/derivative.lisp
new file mode 100644
index 0000000..02fcb4c
--- /dev/null
+++ b/src/approx/derivative.lisp
@@ -0,0 +1,9 @@
+(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))))
diff --git a/src/approx/maceps.lisp b/src/approx/maceps.lisp
new file mode 100644
index 0000000..ad234e8
--- /dev/null
+++ b/src/approx/maceps.lisp
@@ -0,0 +1,11 @@
+(in-package :lizfcm.approx)
+
+(defun compute-maceps (f a init)
+  (let ((h init)
+        (err init))
+    (loop while (> err 0)
+          do
+          (setf h (/ h 2)
+                err (abs (- (funcall f (+ a h))
+                            (funcall f a))))
+          collect (list a h err))))
diff --git a/src/approx/package.lisp b/src/approx/package.lisp
new file mode 100644
index 0000000..c11eb60
--- /dev/null
+++ b/src/approx/package.lisp
@@ -0,0 +1,5 @@
+(in-package :cl-user)
+(defpackage lizfcm.approx
+  (:use :cl)
+  (:export :derivative-at
+           :compute-maceps))