# Taylor series expansion MATLAB Example

# Introduction

In this post, we will learn MATLAB program to compute the Taylor series approximation of a simple function like sin(x). In fact, we can use this approximations to other functions and polynomials.

## Taylor Series

Taylor series of a function f(x) is an infinite series at a point **a** and can be written as :

where

is the nth derivative of the function at point a. The series is also called Maclaurin series when a = 0.

For more information : **https://en.wikipedia.org/wiki/Taylor_series**

### Example

Let’s compute the Taylor series for sin(x) at point a = 0.

Apply the Taylor series expansion formula:

For better understanding of the series lets calculate each term individually for first few terms

The first tern would be =

Second term in the series =

The derivative of sin(x) = cos(x)

The third term in the series =

The second derivative of sin(x) = -sin(x)

The fourth term in the series =

We can ignore the even terms that contain the sin(0) in the series as sin(0) = 0.

We can generalize the series as :

Note that: cos(0) = 1

## MATLAB Program

### Function

function [out] = sinTaylorApprox(x, N) % Input = x, N % out vector : Taylor series approx of sin(x) out=zeros(1,numel(x)); for i = 1 : numel(x) for k = 0: N out(i) = out(i)+ ( (-1)^k * (x(i))^(2*k + 1) ) / factorial(2*k + 1); end end end

## Test Driver Script

Using the defined function to compute the Taylor series approximation for the sin(x), we will create a driver script to plot the graphs for 3rd and 5th order approximations.

The driver script invokes the function twice with input arguments.

% Test Driver Script for plotting Taylor Series Approximation % 2nd order and 4th Order using the function. % MATLAB Tutorials. - www.TestingDocs.com clear close all x = linspace(-2*pi, 2*pi, 100); f = @(x) sin(x); plot(x,f(x),'--rs','LineWidth',1.5,... 'MarkerEdgeColor','k',... 'MarkerFaceColor','g',... 'MarkerSize',9) hold on; grid on; plot(x,sinTaylorApprox(x, 1),'--rs','LineWidth',1.5,... 'MarkerEdgeColor','c',... 'MarkerFaceColor','r',... 'MarkerSize',9) plot(x,sinTaylorApprox(x, 2),'--rs','LineWidth',1.5,... 'MarkerEdgeColor','m',... 'MarkerFaceColor','b',... 'MarkerSize',9) xlabel('x - axis'); ylabel('y - axis'); axis([-6 6 -1 1]) legend('Sin(x) Function', '3rd Order Taylor Approx','5th Order Taylor Approx'); title('Taylor Series Approximation Plot - www.TestingDocs.com'); -

## Approximations Graphs

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