Introduction to Programming in MatlabDr Karen Hampson

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12.10.20

Session Overview

1. What is Matlab?

2. Why Matlab?

3. Navigating the Matlab Environment

4. M-Files

5. Loading data files and plotting

6. Loops

7. Functions

8. Matlab coursework

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1. What is Matlab?Matrix Laboratory

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2. Why Matlab?

• Friendly user interface

• You don’t need to worry about initialising memory forstoring variables or data

• You don’t need to declare the type of a variable

• Widely used in research

• It has many useful toolboxes

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3. Navigating the Matlab Environment

Opening Matlab

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Working Folder – Where to Put Files

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Working Folder – List of Files

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Command Window

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M-Files: Files Containing Code

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Variables

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Demo:Command line as calculatorMatrices in command lineSay can type code here but ‘slow’

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4. M-Files

Simple Program Example

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Adding two numbers together

Variable Name Assigned Value

Lack of ; will cause theoutput to be displayed inthe command window

clear all

NumberOne = 4;

NumberTwo = 3;

TheSum = NumberOne + NumberTwo

Clear any stored variables

Simple Program Example

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Adding two numbers together

Matlab Output

M-File Name

Creating a New M-File

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Executing an M-File

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• Editor tab• Press Run (or F5)• Check you are on

the correct file

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Demo:Open new M-fileShow example program

Program Example

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Adding two numbers together

What do you think would happen in this case?

clear all

TheSum = NumberOne + NumberTwo

NumberOne = 4;

NumberTwo = 3;

Errors

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These display in the command window

Error

Location of Error

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5. Loading Data Files and Plotting

Loading Data Files

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This will form part of the exercises

Txt Files: MyData = load('TheTextFileName.txt');

Image Files: MyImage = imread('TheImageFileName.bmp');

Make sure your files are in the correct directory (i.e. in the Matlab folder)!

(CO01)

(CO01)

Program Example

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Loading data, plotting the data (CO01)

All rows, column 2

Plot the data

clear all

MyData = load('TheTextFileName.txt');

xData = MyData(:,1);

yData = MyData(:,2);

plot(xData,yData)

xlabel('x Variable')

ylabel('y Variable')Label Axis

Program Example

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Loading data, plotting the data (CO01)

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Demo:Open new M-FileLoad and plot data

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6. Loops

For Loop

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Used throughout the coursework exercises

If you only learn one loop – learn this one!

for i = 1:3

DO SOMETHING

end

Do Something 3 times

i = 1;

DO SOMETHING

i = 2;

DO SOMETHING

i = 3;

DO SOMETHING

Program Example

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Summing numbers – SPOT THE ERROR

Notice the indentation.This makes the codeeasier to read.

Print the final value in the command line

VectorOfNumbers = [1 4 6 7 9];

for i = 1:5

Sum = Sum + VectorOfNumbers(i);

end

Sum

Column Vector clear all

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Demo:Open new M-FileRun code with bug

Program Example

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What if the length of the vector changes?

VectorOfNumbers = [1 4 6 7 9];

Sum = 0;

for i = 1:length(VectorOfNumbers)

Sum = Sum + VectorOfNumbers(i);

end

Sum

We don’t want to change the code each time

clear all

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7. Functions

Functions

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Have an input and outputThey take data and perform an action on it

Output = FunctionName(Input)

Creating a New Function

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Creating a New Function

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function [ output_args ] = Untitled( input_args )

end

So Matlabknows it is a function

Code goes here

Name of function

Function Example

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Returning the sum of a set of numbers

function [ TheSum ] = SumTheNumbers( VectorOfNumbers )

Sum = 0;

for i = 1:length(VectorOfNumbers)

Sum = Sum + VectorOfNumbers(i);

end

TheSum = Sum;

end

The output must bedefined somewherein the function

Calling a Function

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Example of calling TheSum function

Create New M-File

VectorOfNumbers = [1 4 6 7 9];

[ TheSum ] = SumTheNumbers( VectorNumbers )

Can you spot the error?

clear all

Function call

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Demo:Create and call function

Calling a Function

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Example of calling TheSum function

Create New M-File

VectorOfNumbers = [ 1 4 6 7 9];

[ TheSum ] = SumTheNumbers( VectorOfNumbers )

Must be the same

Tips/TricksIf you don’t know how to do something, type it in google

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8. Matlab Coursework

The Matlab Coursework

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http://www-teaching.physics.ox.ac.uk/CO-MATLAB/html/course_text.html

REMEMBER TO STORE YOURCODE ON YOUR HOMEDRIVE. NOT ON THE LOCALDRIVE OF THE COMPUTER.

What to Expect During Marking

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CO01 - Grader

Instructions

What to Expect During Marking

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CO01 - Grader

Enter Code

Test Code

Submit

What to Expect During Marking

• You will have to run your code

• You will have to explain your code

• You will need to have a lab book with your programming work inside

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CO02 – In Matlab Environment

Good Coding Practice

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You will be assessed on this

Aim

AuthorDate

What the lines do

What to Expect During Lab Sessions

Demonstrators will online to help you

Thursday 10-1 & 2-5

Friday 10-1 & 2-5

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Each session will have 3-4 demonstrators

What to do if you need more help?

My lab session: Thursday Morning

One-one-one or small group tutorials outside my session or outside Thursday and Friday

Karen.hampson@eng.ox.ac.uk

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Karen.hampson@eng.ox.ac.uk