From 054052144ed8c8d376eb3d72f5057c93b8dcb317 Mon Sep 17 00:00:00 2001
From: Adrian Mariano <avm4@cornell.edu>
Date: Tue, 25 Jun 2024 19:24:48 -0400
Subject: [PATCH] sum/product optimizations

---
 math.scad            | 108 ++++++++++++++++++++++---------------------
 tests/test_math.scad |  12 +++++
 2 files changed, 68 insertions(+), 52 deletions(-)

diff --git a/math.scad b/math.scad
index bb5be7a8..0058d02d 100644
--- a/math.scad
+++ b/math.scad
@@ -721,16 +721,17 @@ function deltas(v, wrap=false) =
 //   cumsum([1,2,3]);  // returns [1,3,6]
 //   cumsum([[1,2,3], [3,4,5], [5,6,7]]);  // returns [[1,2,3], [4,6,8], [9,12,15]]
 function cumsum(v) =
+    v==[] ? [] :
     assert(is_consistent(v), "The input is not consistent." )
-    len(v)<=1 ? v :
-    _cumsum(v,_i=1,_acc=[v[0]]);
-
-function _cumsum(v,_i=0,_acc=[]) =
-   _i>=len(v) ? _acc :
-    _cumsum( v, _i+1, [ each _acc, _acc[len(_acc)-1] + v[_i] ] );
-
-
-
+    [for (a = v[0],
+          i = 1
+            ;
+          i <= len(v)
+            ;
+          a = i<len(v) ? a+v[i] : a,
+          i = i+1)
+        a];
+  
 // Function: product()
 // Synopsis: Returns the multiplicative product of a list of values.
 // Topics: Math, Statistics
@@ -739,24 +740,35 @@ function _cumsum(v,_i=0,_acc=[]) =
 //   x = product(v);
 // Description:
 //   Returns the product of all entries in the given list.
-//   If passed a list of vectors of same dimension, returns a vector of products of each part.
-//   If passed a list of square matrices, returns the resulting product matrix.
+//   If passed a list of vectors of same length, returns a vector of the component-wise products of the input.
+//   If passed a list of square matrices, returns the resulting product matrix.  Matrices are multiplied in the order they appear in the list.
 // Arguments:
 //   v = The list to get the product of.
 // Example:
 //   product([2,3,4]);  // returns 24.
 //   product([[1,2,3], [3,4,5], [5,6,7]]);  // returns [15, 48, 105]
-function product(v) = 
-    assert( is_vector(v) || is_matrix(v) || ( is_matrix(v[0],square=true) && is_consistent(v)), 
-    "Invalid input.")
-    _product(v, 1, v[0]);
-
-function _product(v, i=0, _tot) = 
-    i>=len(v) ? _tot :
-    _product( v, 
-              i+1, 
-              ( is_vector(v[i])? v_mul(_tot,v[i]) : _tot*v[i] ) );
-               
+function product(list,right=true) =
+    list==[] ? [] :
+    is_matrix(list) ?
+                [for (a = list[0], 
+                      i = 1
+                        ;
+                      i <= len(list)
+                        ;
+                      a = i<len(list) ? v_mul(a,list[i]) : 0,
+                      i = i+1)
+                    if (i==len(list)) a][0]
+   :  
+    assert(is_vector(list) || (is_matrix(list[0],square=true) && is_consistent(list)),
+           "Input must be a vector, a list of vectors, or a list of matrices.")
+    [for (a = list[0],
+          i = 1
+            ;
+          i <= len(list)
+            ;
+          a = i<len(list) ? a*list[i] : 0,
+          i = i+1)
+       if (i==len(list)) a][0];
 
 
 // Function: cumprod()
@@ -777,37 +789,29 @@ function _product(v, i=0, _tot) =
 //   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,right=false) =
-   is_vector(list) ? _cumprod(list) :
-   assert(is_consistent(list), "Input must be a consistent list of scalars, vectors or square matrices")
-   assert(is_bool(right))
-   is_matrix(list[0]) ? assert(len(list[0])==len(list[0][0]), "Matrices must be square") _cumprod(list,right) 
-                      : _cumprod_vec(list);
-
-function _cumprod(v,right,_i=0,_acc=[]) = 
-    _i==len(v) ? _acc :
-    _cumprod(
-        v, right, _i+1,
-        concat(
-            _acc,
-            [
-              _i==0 ? v[_i]
-             : right? _acc[len(_acc)-1]*v[_i]
-             : v[_i]*_acc[len(_acc)-1]
-            ]
-        )
-    );
-
-function _cumprod_vec(v,_i=0,_acc=[]) =
-    _i==len(v) ? _acc :
-    _cumprod_vec(
-        v, _i+1,
-        concat(
-            _acc,
-            [_i==0 ? v[_i] : v_mul(_acc[len(_acc)-1],v[_i])]
-        )
-    );
 
+function cumprod(list,right=false) =
+    list==[] ? [] :
+    is_matrix(list) ?
+                [for (a = list[0], 
+                      i = 1
+                        ;
+                      i <= len(list)
+                        ;
+                      a = i<len(list) ? v_mul(a,list[i]) : 0,
+                      i = i+1)
+                    a]
+   :  
+    assert(is_vector(list) || (is_matrix(list[0],square=true) && is_consistent(list)),
+           "Input must be a listector, a list of listectors, or a list of matrices.")
+    [for (a = list[0],
+          i = 1
+            ;
+          i <= len(list)
+            ;
+          a = i<len(list) ? (right ? a*list[i] : list[i]*a) : 0,
+          i = i+1)
+        a];
 
 
 // Function: convolve()
diff --git a/tests/test_math.scad b/tests/test_math.scad
index 64e59ae2..58d67cb7 100644
--- a/tests/test_math.scad
+++ b/tests/test_math.scad
@@ -371,6 +371,7 @@ test_deltas();
 
 
 module test_product() {
+    assert_equal(product([]),[]);
     assert_equal(product([2,3,4]), 24);
     assert_equal(product([[1,2,3], [3,4,5], [5,6,7]]), [15, 48, 105]);
     m1 = [[2,3,4],[4,5,6],[6,7,8]];
@@ -613,6 +614,7 @@ module test_cumprod(){
   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([up(5),down(5)]), [up(5),IDENT]);
   assert_equal(cumprod([
                         [[1,2],[3,4]],
                         [[-4,5],[6,4]],
@@ -623,6 +625,16 @@ module test_cumprod(){
                         [[11,12],[18,28]],
                         [[45,24],[98,132]]
                        ]);
+  assert_equal(cumprod([
+                        [[1,2],[3,4]],
+                        [[-4,5],[6,4]],
+                        [[9,-3],[4,3]]
+                       ],right=true),
+                       [
+                        [[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();