trying to calculate the loss gradient when varying parameters

decons.lisp

@@ -5,7 +5,7 @@
   (:local-nicknames (:shape :scopes/shape)
                     (:util :scopes/util))
   (:export #:rapply #:rreduce #:radd #:rmul #:rsub #:rdiv
-           #:default-deviation #:l2-loss #:trial
+           #:default-deviation #:l2-loss #:trial #:gradient
            #:line
            #:*obj* #:*trials* #:try))
 
@@ -66,6 +66,16 @@
 (defmethod print-object ((tr trial) stream)
   (shape:print-slots tr stream 'theta 'loss))
 
+(defun gradient (target dataset)
+  (let ((expect (funcall (l2-loss target) dataset)))
+    (lambda (theta)
+      (let* ((loss0 (funcall expect theta))
+             (loss1 (funcall expect (vary theta))))
+        (- loss0 loss1)))))
+
+(defun vary (theta)
+  (mapcar (lambda (x) (- x 0.01)) theta))
+
 ;;;; parameterized target functions
 
 (defun line (x)