# 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.

## 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
```