Function addOrder

src/compute-engine/boxed-expression/order.ts:103–123

(a: Expression, b: Expression)

 *
 * E.g.
 * - 2x^2 + 3x + 1
 * - 2x^2y^3 + 5x^3y
 */

export function addOrder(a: Expression, b: Expression): number {
  const aTotalDeg = totalDegree(a);
  const bTotalDeg = totalDegree(b);
  if (aTotalDeg !== bTotalDeg) return bTotalDeg - aTotalDeg;

  const aMaxDeg = maxDegree(a);
  const bMaxDeg = maxDegree(b);
  if (aMaxDeg !== bMaxDeg) return bMaxDeg - aMaxDeg;

  // Get a lexicographic key of the expression
  // i.e. `xy^2` -> `x y`
  const aLex = revlex(a);
  const bLex = revlex(b);
  if (aLex || bLex) {
    if (!aLex) return +1;
    if (!bLex) return -1;
    if (aLex < bLex) return -1;
    if (aLex > bLex) return +1;
  }
  return order(a, b);