mathjs/src/function/arithmetic/log.js

'use strict'

import { factory } from '../../utils/factory'
import { deepMap } from '../../utils/collection'

const name = 'log'
const dependencies = ['config.predictable', 'typed', 'divideScalar', 'type.Complex']

export const createLog = /* #__PURE__ */ factory(name, dependencies, ({ typed, config, divideScalar, type: { Complex } }) => {
  /**
   * Calculate the logarithm of a value.
   *
   * For matrices, the function is evaluated element wise.
   *
   * Syntax:
   *
   *    math.log(x)
   *    math.log(x, base)
   *
   * Examples:
   *
   *    math.log(3.5)                  // returns 1.252762968495368
   *    math.exp(math.log(2.4))        // returns 2.4
   *
   *    math.pow(10, 4)                // returns 10000
   *    math.log(10000, 10)            // returns 4
   *    math.log(10000) / math.log(10) // returns 4
   *
   *    math.log(1024, 2)              // returns 10
   *    math.pow(2, 10)                // returns 1024
   *
   * See also:
   *
   *    exp, log2, log10, log1p
   *
   * @param {number | BigNumber | Complex | Array | Matrix} x
   *            Value for which to calculate the logarithm.
   * @param {number | BigNumber | Complex} [base=e]
   *            Optional base for the logarithm. If not provided, the natural
   *            logarithm of `x` is calculated.
   * @return {number | BigNumber | Complex | Array | Matrix}
   *            Returns the logarithm of `x`
   */
  const log = typed(name, {
    'number': function (x) {
      if (x >= 0 || config.predictable) {
        return Math.log(x)
      } else {
        // negative value -> complex value computation
        return new Complex(x, 0).log()
      }
    },

    'Complex': function (x) {
      return x.log()
    },

    'BigNumber': function (x) {
      if (!x.isNegative() || config.predictable) {
        return x.ln()
      } else {
        // downgrade to number, return Complex valued result
        return new Complex(x.toNumber(), 0).log()
      }
    },

    'Array | Matrix': function (x) {
      return deepMap(x, log)
    },

    'any, any': function (x, base) {
      // calculate logarithm for a specified base, log(x, base)
      return divideScalar(log(x), log(base))
    }
  })

  return log
})