4 files changed, 21 insertions, 0 deletions
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))))
diff --git a/cl/src/approx/package.lisp b/cl/src/approx/package.lisp
new file mode 100644
index 0000000..60dd0bb
--- /dev/null
+++ b/cl/src/approx/package.lisp
@@ -0,0 +1,4 @@
+(in-package :cl-user)
+(defpackage lizfcm.approx
+  (:use :cl)
+  (:export :derivative-at))
diff --git a/cl/src/utils/package.lisp b/cl/src/utils/package.lisp
new file mode 100644
index 0000000..0436a94
--- /dev/null
+++ b/cl/src/utils/package.lisp
@@ -0,0 +1,4 @@
+(in-package :cl-user)
+(defpackage lizfcm.utils
+  (:use :cl)
+  (:export :within-range-p))
diff --git a/cl/src/utils/within-range.lisp b/cl/src/utils/within-range.lisp
new file mode 100644
index 0000000..9a0b762
--- /dev/null
+++ b/cl/src/utils/within-range.lisp
@@ -0,0 +1,5 @@
+(in-package :lizfcm.utils)
+
+(defun within-range-p (x true-value delta)
+  (and (< x (+ true-value delta))
+       (> x (- true-value delta))))