mathjs/src/function/algebra/simplify/util.js

Math.js is an extensive math library for JavaScript and Node.js. It features a flexible expression parser with support for symbolic computation, comes with a large set of built-in functions and constants, and offers an integrated solution to work with dif

import { isOperatorNode } from '../../../utils/is'
import { factory } from '../../../utils/factory'
import { hasOwnProperty } from '../../../utils/object'

const name = 'simplifyUtil'
const dependencies = [
  'FunctionNode',
  'OperatorNode',
  'SymbolNode'
]

export const createUtil = /* #__PURE__ */ factory(name, dependencies, ({ FunctionNode, OperatorNode, SymbolNode }) => {
  // TODO commutative/associative properties rely on the arguments
  // e.g. multiply is not commutative for matrices
  // The properties should be calculated from an argument to simplify, or possibly something in math.config
  // the other option is for typed() to specify a return type so that we can evaluate the type of arguments
  const commutative = {
    add: true,
    multiply: true
  }
  const associative = {
    add: true,
    multiply: true
  }

  function isCommutative (node, context) {
    if (!isOperatorNode(node)) {
      return true
    }
    const name = node.fn.toString()
    if (context && hasOwnProperty(context, name) && hasOwnProperty(context[name], 'commutative')) {
      return context[name].commutative
    }
    return commutative[name] || false
  }

  function isAssociative (node, context) {
    if (!isOperatorNode(node)) {
      return false
    }
    const name = node.fn.toString()
    if (context && hasOwnProperty(context, name) && hasOwnProperty(context[name], 'associative')) {
      return context[name].associative
    }
    return associative[name] || false
  }

  /**
   * Flatten all associative operators in an expression tree.
   * Assumes parentheses have already been removed.
   */
  function flatten (node) {
    if (!node.args || node.args.length === 0) {
      return node
    }
    node.args = allChildren(node)
    for (let i = 0; i < node.args.length; i++) {
      flatten(node.args[i])
    }
  }

  /**
   * Get the children of a node as if it has been flattened.
   * TODO implement for FunctionNodes
   */
  function allChildren (node) {
    let op
    const children = []
    const findChildren = function (node) {
      for (let i = 0; i < node.args.length; i++) {
        const child = node.args[i]
        if (isOperatorNode(child) && op === child.op) {
          findChildren(child)
        } else {
          children.push(child)
        }
      }
    }

    if (isAssociative(node)) {
      op = node.op
      findChildren(node)
      return children
    } else {
      return node.args
    }
  }

  /**
   *  Unflatten all flattened operators to a right-heavy binary tree.
   */
  function unflattenr (node) {
    if (!node.args || node.args.length === 0) {
      return
    }
    const makeNode = createMakeNodeFunction(node)
    const l = node.args.length
    for (let i = 0; i < l; i++) {
      unflattenr(node.args[i])
    }
    if (l > 2 && isAssociative(node)) {
      let curnode = node.args.pop()
      while (node.args.length > 0) {
        curnode = makeNode([node.args.pop(), curnode])
      }
      node.args = curnode.args
    }
  }

  /**
   *  Unflatten all flattened operators to a left-heavy binary tree.
   */
  function unflattenl (node) {
    if (!node.args || node.args.length === 0) {
      return
    }
    const makeNode = createMakeNodeFunction(node)
    const l = node.args.length
    for (let i = 0; i < l; i++) {
      unflattenl(node.args[i])
    }
    if (l > 2 && isAssociative(node)) {
      let curnode = node.args.shift()
      while (node.args.length > 0) {
        curnode = makeNode([curnode, node.args.shift()])
      }
      node.args = curnode.args
    }
  }

  function createMakeNodeFunction (node) {
    if (isOperatorNode(node)) {
      return function (args) {
        try {
          return new OperatorNode(node.op, node.fn, args, node.implicit)
        } catch (err) {
          console.error(err)
          return []
        }
      }
    } else {
      return function (args) {
        return new FunctionNode(new SymbolNode(node.name), args)
      }
    }
  }

  return {
    createMakeNodeFunction,
    isCommutative,
    isAssociative,
    flatten,
    allChildren,
    unflattenr,
    unflattenl
  }
})