Basics of programming in matlab for beginners

Basics of Matlab Programming
Opio Phillip
Mountains of the Moon University
popio@mmu.ac.ug

MATLAB:- MATrix LABoratory
▸ Developed by Mathworks, Inc. http://www.mathworks.com
▸ It is an interactive, integrated, environment
▸ for numerical/symbolic, scientific computations and other
Apps
▸ shorter program development and debugging time than
other languages such as FORTRAN and C
▸ slow compared to FORTRAN or C
▸ easy to use
▸ automatic memory management; no need to declare
arrays
▸ etc

Getting Started with MATLAB
▸ Windows
double click MATLAB icon
▸ Linux Cluster
cd to bin folder in the installation dir
then ./matlab
▸ Either case it opens a MATLAB window with >> prompt
▸ To stop, type quit or exit at the command prompt >>

Current Folder
Files in the
current folder
Work Space
a 4
b 6
c 10
Command Window
Input Commands at the command line
prompt ≫
eg.
≫ a= 4;
≫ b=6;
≫ c=a+b;

Variable and File Names
▸ case sensitive, e.g., fname and fName are different names
▸ can be a mix of letters, digits, and underscores (e.g.,
vector A)
▸ variable namws always start with a letter e.g., xy or x2y
▸ maximum of 63 characters
▸ reserved characters: % = + - ; : ’ [ ] ( ) , # $ &
ˆ ! ∼ can NOT be used
▸ No space in the names e.g class marks not allowed

Uses of the characters % = ; ,
▸ % for adding comments, %% creates a shell in mfile
▸ = to asign a value to a variable e.g c=10
▸ ;
(i) suppresses output in the command window
(ii) delimits commands in the same line e.g clear;close all;
a=4;b=5;
(iii) seperate rows e.g. d=[2;3;4];
▸ ,
(i) seperate columns e = [4,2,3,1];
(ii) delimits commands in the same line e.g k = 4,m=12

Uses of the characters [] () :
▸ []
(i) for arrays e.g p =[12,3]
(ii) delete contents of arrays e.g x = [] deletes contents of x
▸ ()
(i) matrix indexing e.g t =[2,3,4], s=t(1,2)
(ii) inputs of functions e.g z = mean(t)
▸ :
(i) creating a row vector eg. A = 1:5; B = 0:2:10;
(ii) select in a range or all e.g. C= A(1,1:3); D = A(:,:)
(iii) reshape a matrix to a column eg. E = A(:);

Uses of the characters ... ’ ! ∼
▸ ... used to continue the code in the next line
1 if length(a) <5
2 a = [1,2,3,...
3 4,5];
4 end% end for the if condition
▸ ’
(i) to transpose e.g. t =[2,3,4]; s=t’;
(ii) create strings e.g. z = ’Hello’;
▸ ∼ means not e.g. is not equal ∼=
▸ ! same as system

Creation of Arrays
1 % A row vector: use the column seperator
, or space
2 A = [1,2,3,4,5,6];
3
4 % A column vector: use the row seperator ,
;
5 D1 = [2;4;5;6];
6
7 % Matrices of many columns and rows
8 C1 = [2,4,6;2,3,5;1,NaN ,3];
9 C2 =[C1;C1];

Special Matrices
1 % Identity matrix of n by n
2 I = eye (4);
3
4 % Matrix of ones: ones(raws ,columns)
5 D1 = ones (2,5);
6
7 % Matrix of zeros: zeros(raws ,columns)
8 E1 = zeros (5 ,31);
9
10 % n by n magic square matrices
11 M = magic (3);

Matrix Operations
▸ Transpose of A - A’
▸ Inverse of A - inv(A)
▸ multiplication- A*A
▸ element-wise multiplication- A.*A
▸ For a linear equation, Ax = b;
1 x=Ab;
▸ Concatenation
▸ Horz. Concatenation - Number of raws must be the same
Hcon=[A,A] or [A A]
▸ Vert. Concatenation - Number of columns must be the same
Vcon=[A;A]

Matrix Indexing - access a particular element(s) in a matrix.
A = [10 21; 41 51; 32 19];
▸ to access an element
new matrix = A(row index,column index)
eg. A new=A(3,2)
▸ select a number of rows and columns
new matrix = A([row numbers],[column numbers])
eg. B new=A([2 3],[1 2])
▸ deleting a raw or column elements
A([raw numbers],[column numbers])=[]
A(1,:)=[]

Matrix Indexing ...
▸ Replace an element
A(raw index,column index) = new number
eg. A(2,3)=100;
▸ Replace a set of number eg numbers > 5
A(A>5) = new number
eg. A(A>5)=NaN;
▸ finding indices for numbers
index=find(A>5)
A(index)=5

Conditional Statements (if, elseif, else )
▸ if statements, expressions end
eg. doy= 9
if doy < 10
DOY=['00' int2str(doy)];
end
▸ if statements, expressions elseif statements, expressions else
statements, expressions end
if doy<10
DOY=['00' num2str(doy)];
elseif doy>9 && doy<100
DOY=['0' num2str(doy)];
else
DOY=int2str(doy);
end

Conditional statements ... (switch, case, otherwise)
▸ switch switch expression
case case expression
statements, expresions
...
otherwise
statements,expresions
end
eg. igs_station='MBAR'
switch igs station
case 'MBAR'
lon=30.74;lat=-0.6;
case 'EBBE'
lon=32.54;lat=0.04;
otherwise
lon=NaN; lat=NaN;
end

Loops (for and while)
▸ for MATLAB commands end
eg. s= 0; triglenumber=[];
for i1=1:20
s=s+i1;
if mod(s,2)==0
continue
end
triglenumber=[triglenumber;s];
end

while loop
1 z = 'Mbar009 -2000 -12 -13. txt';
2 x = [];
3 i = 1;
4 while isempty(x)
5 pt = z(1:i);
6 x= strfind(pt ,'.');
7 i=i+1;
8
9 end
10 sprintf(pt)

Data Properties
▸ properties of the workspace variables are accessed by
typing whos at command the prompt >>
e.g >> whos
Name Size Bytes Class Attributes
data1 2x3 50 single
data2 100x345 5000 double
data3 1x35 55 cell
data4 12x34 400 char
data5 10x5 58 struc

string - characters enclosed in single quotes.
eg. mytext='Hello world';
▸ Concatenate strings like in Matrices
eg. text=[mytext(1:5) 'my friend'];
▸ convert numeric values to strings - useful in labeling plots
use int2str(numeric value) or num2str(numeric value)
eg. datadir=['/home/andima/data/' int2str(2008) '/Cmn/' ]
▸ Format data into string using sprintf
yr=2008;doy=3
eg. daydir=sprintf('igs/%i/00%i',yr,doy);

Cell Arrays - Each element may point to a scalar, an array, or
another cell array.
eg. C=cell(2, 3)%create 2x3 empty cell array
M = magic(2);
a = 1:3; b = [4;5;6]; s = ’This is a string’;
C{1,1} = M;
C{1,2} = a;
C{2,1} = b;
C{2,2} = s;
▸ Some of the useful functions for cells include
iscell, cell2mat

Structure - good for grouping arrays that are related.
eg. name(1).last = ‘Smith’;name(2).last = ‘Hess’;
name(1).first = ‘Mary’; name(2).first = ‘Robert’;
name(1).sex = ‘female’; name(2).sex = ‘male’;
▸ Alternatively
name = struct(‘last’,Smith’,’Hess’,...,
‘first’,Mary’,’Robert’,‘sex’,female’,’male’);
▸ Related utilities: isstruct, fieldnames, getfield, isfield

File types
▸ script m-files (.m): commands that reside in the base of
workspace
▸ function m-files (.m): memory access controlled;
parameters passed as input, output arguments; reside in
own workspace
▸ mat files (.mat): binary or text files handled with save and
load
▸ mex files (.mex): runs C/FORTRAN codes from m-file;
▸ eng files (.eng): runs m-file from C/FORTRAN code
▸ C codes (.c): generated by MATLAB compiler
▸ P codes (.p): converted m-files to hide source for security

Script m-file
If you have a group of commands that are expected to be
executed repeatedly, it is convenient to save them in a file
▸ enter commands in editor
▸ Save as a *.m file
▸ A script shares the same scope with that which it operates.

Function m-files
▸ It is declared with the key word function, with optional
input parameters on the right and optional output on the
left of = sign
▸ all other parameters within function reside in function’s
own workspace.
▸ created in the MATLAB editor. e.g.
1 function M = my_mean(x)
2 M=sum(x)/numel(x);
3 end
▸ funtions may be called from a script, another function, or
on command line

Importing data into MATLAB
Many functions are available to import data into matlab. The
choice depends on the nature of the data. Some of these
functions include
▸ load:
▸ used to import data without text in it. eg
1 filename = 'mbar034 -2015 -02 -03. txt';
2 Data = load(filename);

reading data using fgetl
▸ fgetl: used to read each line of the data
1 filename = 'mbar002 -2015 -01 -02. Cmn';
fid = fopen(filename);
2 eof = 'Jdatet ';header =[];
3
4 while isempty(header)
5 line1 = fgetl(fid);
6 header = strfind(line1 ,eof);
7 end

reading data using textscan
▸ textscan: used to read each line of the data
1 filename = 'mbar002 -2015 -01 -02. Cmn';
fid = fopen(filename);
2 eof = 'Jdatet ';header =[];
3
4 while isempty(header)
5 line1 = fgetl(fid);
6 header = strfind(line1 ,eof);
7 end
8 Data = textscan(fid);

Basics of programming in matlab for beginners

More Related Content

Similar to Basics of programming in matlab for beginners (20)

Recently uploaded (20)

Basics of programming in matlab for beginners