Many students ask me how do I do this or that in MATLAB. So I thought why not have a small series of my next few blogs do that. In this blog I show you how to differentiate a function.

The MATLAB program link is here.

The HTML version of the MATLAB program is here.

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%% 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

%% INTRODUCTION

clc

clear all

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 https://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(‘ ‘)

%% 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(‘ ‘)

%% 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(‘ ‘)

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This post is brought to you by Holistic Numerical Methods: Numerical Methods for the STEM undergraduate at http://numericalmethods.eng.usf.edu, the textbook on Numerical Methods with Applications available from the lulu storefront, and the YouTube video lectures available at http://numericalmethods.eng.usf.edu/videos and http://www.youtube.com/numericalmethodsguy

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