From f598426344099b13f89e78716ee1be27616a14f6 Mon Sep 17 00:00:00 2001
From: Adrian Mariano <avm4@cornell.edu>
Date: Fri, 23 Oct 2020 19:06:30 -0400
Subject: [PATCH] Add cumprod function and regression test

---
 math.scad            | 38 ++++++++++++++++++++++++++++++++++++++
 tests/test_math.scad | 22 ++++++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/math.scad b/math.scad
index c0ac6ab..6cb1362 100644
--- a/math.scad
+++ b/math.scad
@@ -617,6 +617,44 @@ function _product(v, i=0, _tot) =
                
 
 
+// Function: cumprod()
+// Description:
+//   Returns a list where each item is the cumulative product of all items up to and including the corresponding entry in the input list.
+//   If passed an array of vectors, returns a list of elementwise vector products.  If passed a list of square matrices returns matrix
+//   products multiplying in the order items appear in the list.  
+// Arguments:
+//   list = The list to get the product of.
+// Example:
+//   cumprod([1,3,5]);  // returns [1,3,15]
+//   cumprod([2,2,2]);  // returns [2,4,8]
+//   cumprod([[1,2,3], [3,4,5], [5,6,7]]));  // returns [[1, 2, 3], [3, 8, 15], [15, 48, 105]]
+function cumprod(list) =
+   is_vector(list) ? _cumprod(list) :
+   assert(is_consistent(list), "Input must be a consistent list of scalars, vectors or square matrices")
+   is_matrix(list[0]) ? assert(len(list[0])==len(list[0][0]), "Matrices must be square") _cumprod(list) 
+                      : _cumprod_vec(list);
+
+function _cumprod(v,_i=0,_acc=[]) =
+    _i==len(v) ? _acc :
+    _cumprod(
+        v, _i+1,
+        concat(
+            _acc,
+            [_i==0 ? v[_i] : _acc[len(_acc)-1]*v[_i]]
+        )
+    );
+
+function _cumprod_vec(v,_i=0,_acc=[]) =
+    _i==len(v) ? _acc :
+    _cumprod_vec(
+        v, _i+1,
+        concat(
+            _acc,
+            [_i==0 ? v[_i] : vmul(_acc[len(_acc)-1],v[_i])]
+        )
+    );
+
+
 // Function: outer_product()
 // Usage:
 //   x = outer_product(u,v);
diff --git a/tests/test_math.scad b/tests/test_math.scad
index 824098a..1d9fee9 100644
--- a/tests/test_math.scad
+++ b/tests/test_math.scad
@@ -836,6 +836,28 @@ module test_linear_solve(){
 test_linear_solve();
 
 
+module test_cumprod(){
+  assert_equal(cumprod([1,2,3,4]), [1,2,6,24]);
+  assert_equal(cumprod([4]), [4]);
+  assert_equal(cumprod([]),[]);
+  assert_equal(cumprod([[2,3],[4,5],[6,7]]), [[2,3],[8,15],[48,105]]);
+  assert_equal(cumprod([[5,6,7]]),[[5,6,7]]);
+  assert_equal(cumprod([
+                        [[1,2],[3,4]],
+                        [[-4,5],[6,4]],
+                        [[9,-3],[4,3]]
+                       ]),
+                       [
+                        [[1,2],[3,4]],
+                        [[8,13],[12,31]],
+                        [[124,15],[232,57]]
+                       ]);
+  assert_equal(cumprod([[[1,2],[3,4]]]), [[[1,2],[3,4]]]);
+}
+test_cumprod();
+                         
+
+
 module test_outer_product(){
   assert_equal(outer_product([1,2,3],[4,5,6]), [[4,5,6],[8,10,12],[12,15,18]]);
   assert_equal(outer_product([1,2],[4,5,6]), [[4,5,6],[8,10,12]]);