# HOW DO I DO THAT IN MATLAB SERIES?

In this series, I am answering questions that students have asked me about MATLAB. Most of the questions relate to a mathematical procedure.

## Contents

## TOPIC

How do I differentiate a function?

## SUMMARY

% Language : Matlab 2008a; % Authors : Autar Kaw; % Mfile available at % <http://numericalmethods.eng.usf.edu/blog/differentiation.m>; % Last Revised : March 21, 2009; % Abstract: This program shows you how to differentiate a given function. clc clear all

## INTRODUCTION

disp('ABSTRACT') disp(' This program shows you how to differentiate') disp(' a given function and then find its value') disp(' at a given point') disp(' ') disp('AUTHOR') disp(' Autar K Kaw of http://autarkaw.wordpress.com') disp(' ') disp('MFILE SOURCE') disp(' http://numericalmethods.eng.usf.edu/blog/differentiation.m') disp(' ') disp('LAST REVISED') disp(' March 21, 2009') disp(' ')

ABSTRACT This program shows you how to differentiate a given function and then find its value at a given point AUTHOR Autar K Kaw of http://autarkaw.wordpress.com MFILE SOURCE http://numericalmethods.eng.usf.edu/blog/differentiation.m LAST REVISED March 21, 2009

## INPUTS

% Differentiate 7 exp(3*x) once and find the value of the % first derivative at x=0.5 % Define x as a symbol syms x % Defining the function to be differentiated y=7*exp(3*x); % Defining the point where you want to find the derivative xx=0.5;

## DISPLAYING INPUTS

disp('INPUTS') func=[' The function is to be differentiated is ' char(y)]; disp(func) fprintf(' Value of x where you want to find the derivative, x= %g',xx) disp(' ') disp(' ')

INPUTS The function is to be differentiated is 7*exp(3*x) Value of x where you want to find the derivative, x= 0.5

## THE CODE

% Finding the derivative using the diff command % Argument 1 is the function to be differentiated % Argument 2 is the variable with respect to which the % function is to be differentiated - the independent variable % Argument 3 is the order of derivative dydx=diff(y,x,1); % subs command substitues the value of x dydx_val=subs(dydx,x,xx);

## DISPLAYING OUTPUTS

disp('OUTPUTS') derivative_func=[' The derivative of function ' char(y) ' is ' char(dydx)]; disp(derivative_func) fprintf(' Value of dydx at x=%g is =%g',xx,dydx_val) disp(' ')

OUTPUTS The derivative of function 7*exp(3*x) is 21*exp(3*x) Value of dydx at x=0.5 is =94.1155