reorganize directory and file structure

extra/point/nominal.js

@@ -0,0 +1,23 @@
+export const cart2polar = ({x, y}) => {
+  const r = Math.sqrt(x*x + y*y);
+  const θ = Math.atan(y/x);
+  return {r, θ};
+};
+
+export const polar2cart = ({r, θ}) => {
+  const x = r * Math.cos(θ);
+  const y = r * Math.sin(θ);
+  return {x, y};
+}
+
+export const translate = dx => dy => ({x, y}) => {
+  return {left: x+dx, right: y+dy};
+}
+
+export const rotate = dθ => ({r, θ}) => {
+  return {r, θ: θ+dθ};
+}
+
+export const scale = dr => ({r, θ}) => {
+  return {r: r+dr, θ};
+}