forwardjs-ml-math-lodash.js

const map = require('lodash/map')
const reduce = require('lodash/reduce')

const validateLengths = (a,b,action) => {
  if (a.length !== b.length) {
    throw Error(`Can\'t ${action} arrays of length ${a.length} and ${b.length}`);
  }
}

const arrayMultiply = (arr1, arr2) => {
  validateLengths(arr1, arr2, "multiply")
  return reduce(arr1, (accumulator, arrayItem, i) =>
    accumulator += arrayItem * arr2[i]
  , 0)
}

const arrayAdd = (arr1, arr2) => {
  validateLengths(arr1, arr2, "add")
  return map(arr1, (arrayItem, i) =>
    arrayItem + arr2[i]
  )
}

const arraySubtract = (arr1, arr2) => {
  validateLengths(arr1, arr2, "subtract")
  return map(arr1, (arrayItem, i) =>
    arrayItem - arr2[i]
  )
}

const sigmoid = (z) =>
  1 / (1 + Math.exp(z * -1))

const sigmoidGradient = (z) =>
  sigmoid(z) * (1 - sigmoid(z))

const sigmoidInverse = (a) =>
  Math.log(a) - Math.log(1 - a)

exports.arrayMultiply = arrayMultiply;
exports.arrayAdd = arrayAdd;
exports.arraySubtract = arraySubtract;
exports.sigmoid = sigmoid;
exports.sigmoidGradient = sigmoidGradient;
exports.sigmoidInverse = sigmoidInverse;

@jedborovik Thanks for amazing workshop!
As a way to integrate the learning I've been working through the codebase and rewriting stuff in lodash and ES6.

Saw some nice performance gains in math module
First run uses regular lib, 2nd run uses this version

is there a repo I can make a PR?

PS. haven't tested for any regressions other than getting similar output from the network