diff --git a/src/algorithms/math/horner-method/README.md b/src/algorithms/math/horner-method/README.md new file mode 100644 index 00000000..719257b3 --- /dev/null +++ b/src/algorithms/math/horner-method/README.md @@ -0,0 +1,21 @@ +# Horner's Method + +In mathematics, Horner's method (or Horner's scheme) is an algorithm for polynomial evaluation. +With this method, it is possible to evaluate a polynomial with only n additions and n multiplications. +Hence, its storage requirements are n times the number of bits of x. + +Horner's method can be based on the following identity: +![](https://wikimedia.org/api/rest_v1/media/math/render/svg/2a576e42d875496f8b0f0dda5ebff7c2415532e4) +, which is called Horner's rule. + +To solve the right part of the identity above, for a given x, we start by iterating through the polynomial from the inside out, +accumulating each iteration result. After n iterations, with n being the order of the polynomial, the accumulated result gives +us the polynomial evaluation. + +Using the polynomial: +![](http://www.sciweavers.org/tex2img.php?eq=%244x%5E4%20%2B%202x%5E3%20%2B%203x%5E2%2B%20x%5E1%20%2B%203%24&bc=White&fc=Black&im=jpg&fs=12&ff=arev&edit=0), a traditional approach to evaluate it at x = 2, could be representing it as an array [3,1,3,2,4] and iterate over it saving each iteration value at an accumulator, such as acc += pow(x=2,index) * array[index]. In essence, each power of a number (pow) operation is n-1 multiplications. So, in this scenario, a total of 15 operations would have happened, composed of 5 additions, 5 multiplications, and 5 pows. + +Now, using the same scenario but with Horner's rule, the polynomial can be re-written as ![](http://www.sciweavers.org/tex2img.php?eq=%24x%28x%28x%284x%2B2%29%2B3%29%2B1%29%2B3%24&bc=White&fc=Black&im=jpg&fs=12&ff=arev&edit=0), representing it as [4,2,3,1,3] it is possible to save the first iteration as acc = arr[0]*(x=2) + arr[1], and then finish iterations for acc *= (x=2) + arr[index]. In the same scenario but using Horner's rule, a total of 10 operations would have happened, composed of only 5 additions and 5 multiplications. +## References + +- [Wikipedia](https://en.wikipedia.org/wiki/Horner%27s_method) diff --git a/src/algorithms/math/horner-method/__test__/hornerMethod.test.js b/src/algorithms/math/horner-method/__test__/hornerMethod.test.js new file mode 100644 index 00000000..85d74bbc --- /dev/null +++ b/src/algorithms/math/horner-method/__test__/hornerMethod.test.js @@ -0,0 +1,14 @@ +import hornerMethod from '../hornerMethod'; + +describe('hornerMethod', () => { + it('should evaluate the polynomial on the specified point correctly', () => { + expect(hornerMethod([8],0.1)).toBe(8); + expect(hornerMethod([2,4,2,5],0.555)).toBe(7.68400775); + expect(hornerMethod([2,4,2,5],0.75)).toBe(9.59375); + expect(hornerMethod([1,1,1,1,1],1.75)).toBe(20.55078125); + expect(hornerMethod([15,3.5,0,2,1.42,0.41],0.315)).toBe(1.136730065140625); + expect(hornerMethod([0,0,2.77,1.42,0.41],1.35)).toBe(7.375325000000001); + expect(hornerMethod([0,0,2.77,1.42,2.3311],1.35)).toBe(9.296425000000001); + expect(hornerMethod([2,0,0,5.757,5.31412,12.3213],3.141)).toBe(697.2731167035034); + }); +}); \ No newline at end of file diff --git a/src/algorithms/math/horner-method/hornerMethod.js b/src/algorithms/math/horner-method/hornerMethod.js new file mode 100644 index 00000000..11b029f8 --- /dev/null +++ b/src/algorithms/math/horner-method/hornerMethod.js @@ -0,0 +1,17 @@ +/** + * Returns the evaluation of a polynomial function at a certain point. + * Uses Horner's rule. + * @param {number[]} numbers + * @return {number} + */ +export default function hornerMethod(numbers, point) { + // polynomial function is just a constant. + if (numbers.length === 1) { + return numbers[0]; + } + return numbers.reduce((accumulator, currentValue, index) => { + return index === 1 + ? numbers[0] * point + currentValue + : accumulator * point + currentValue; + }); +}