add doc

README.md

@@ -404,6 +404,12 @@ These examples incubate dotSCAD and dotSCAD refactors these examples. See [examp
 --|--
 [**matrix/m_replace**(m, i, j, value)](https://openhome.cc/eGossip/OpenSCAD/lib3x-m_replace.html) | replace the aᵢⱼ element of a matrix.
 
+## Triangle
+
+ Signature | Description
+--|--
+[**triangle/tri_subdivide**(shape_pts[, n])](https://openhome.cc/eGossip/OpenSCAD/lib3x-tri_subdivide.html) | subdivide a triangle `n` times.
+
 ## Point Picking
 
  Signature | Description

docs/lib3x-tri_subdivide.md

@@ -0,0 +1,31 @@
+# tri_subdivide
+
+Subdivide a triangle `n` times.
+
+**Since:** 3.3
+
+## Parameters
+
+- `shape_pts` : the vertices of a 2D or 3D triangle.
+- `n` : subdivide a triangle `n` times. Default to 1.
+
+## Examples
+
+    use <shape_circle.scad>
+    use <triangle/tri_subdivide.scad>
+   
+    radius = 10;
+    tri = shape_circle(radius, $fn = 3);
+    
+    polygon(tri);
+    
+    for(n = [1:3]) {
+        subdivided = tri_subdivide(tri, n);
+        translate([radius * 2 * n, 0])
+        for(t = subdivided) {
+            offset(-.1)
+                polygon(t);
+        }
+    }
+
+![tri_subdivide](images/lib3x-tri_subdivide-1.JPG)

src/experimental/note.md

@@ -4,8 +4,6 @@ to_do:
 
 new:
 
-- triangle/tri_subdivide
-
 - mz_hamiltonian supports init_cells
 
    update doc mz_square_initialize
@@ -33,4 +31,6 @@ doc-ed
     - util/sorted, util/binary_search, util/contains
     - maze/mz_square, maze/mz_theta, maze/mz_squarewalls, maze/mz_hexwalls, maze/mz_tiles
     - matrix/m_replace
+    - triangle/tri_subdivide
+
     

src/triangle/tri_subdivide.scad

@@ -1,6 +1,16 @@
+/**
+* tri_subdivide.scad
+*
+* @copyright Justin Lin, 2022
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib3x-tri_subdivide.html
+*
+**/
+
 use <_impl/_tri_subdivide_impl.scad>
     
-function tri_subdivide(shape_pts, n) =
+function tri_subdivide(shape_pts, n = 1) =
     n == 0 ? [shape_pts] :
     let(
         pts = _tri_subdivide_pts(shape_pts, n + 1),