1 Introduction to Matlab

2 What is Matlab? Matlab is basically a high level language which has many specialized toolboxes for making things easier for us MATLAB is a high-level language and interactive environment that enables us to perform computationally intensive tasks faster than with traditional programming languages such as C, C++, and Fortran. How high? Assembly High Level Languages such as C, Pascal etc. Matlab

3 Matlab Desktop Command Window Launch Pad History

4 Matlab Desktop – cont’d Command Window Workspace Current DIrectory

5 Matlab Help

6 Matlab Programs Matlab is an extravagant calculator if all we can do is execute commands typed into the Command Window… So how can we execute a “program?” Programs in Matlab are: –Scripts, or –Functions Scripts: Matlab statements that are fed from a file into the Command Window and executed immediately Functions: Program modules that are passed data (arguments) and return a result (i.e., sin(x)) These can be created in any text editor (but Matlab supplies a nice built-in editor)

7 Matlab Editor Color keyed text with auto indents tabbed sheets for other files being edited Access to commands

8 The Matlab Environment Matlab is an interpreted language –Commands are typed into the COMMAND Window and executed immediately –Variables are allocated in memory as soon as they are first used in an expression –Commands must be re-entered to be re-executed All variables created in the Command Window are in what is called the Base Workspace –Variables can be reassigned new values as needed –Variables can be selectively cleared from the workspace The Workspace can be saved to a data file –File extension is.mat (ex: mydata.mat) –File is in binary and essentially unreadable by humans –.mat files can be reloaded back into the Matlab Workspace

9 Reserved Words… Matlab has some special (reserved) words that you may not use… for end if while function return elseif case otherwise switch continue else try catch global persistent break

10 Variables No need for types. i.e., All variables are created with double precision unless specified and they are matrices. After these statements, the variables are 1x1 matrices with double precision int a; double b; float c; Example: >>x=5; >>x1=2;

11 Array, Matrix a vector x = [ ] x = a matrix x = [1 2 3; 5 1 4; ] x = transpose y = x’ y =

12 Long Array, Matrix t =1:10 t = k =2:-0.5:-1 k = B = [1:4; 5:8] x =

13 Generating Vectors from functions zeros(M,N)MxN matrix of zeros ones(M,N)MxN matrix of ones rand(M,N)MxN matrix of uniformly distributed random numbers on (0,1) x = zeros(1,3) x = x = ones(1,3) x = x = rand(1,3) x =

14 Matrix Index The matrix indices begin from 1 (not 0 (as in C)) The matrix indices must be positive integer Given: A(-2), A(0) Error: ??? Subscript indices must either be real positive integers or logicals. A(4,2) Error: ??? Index exceeds matrix dimensions.

15 Concatenation of Matrices x = [1 2], y = [4 5], z=[ 0 0] A = [ x y] B = [x ; y] C = [x y ;z] Error: ??? Error using ==> vertcat CAT arguments dimensions are not consistent.

16 Operators (arithmetic) +addition -subtraction *multiplication /division ^power ‘complex conjugate transpose

17 Matrices Operations Given A and B: AdditionSubtractionProductTranspose

18 Operators (Element by Element).*element-by-element multiplication./element-by-element division.^element-by-element power

19 The use of “.” – “Element” Operation K= x^2 Erorr: ??? Error using ==> mpower Matrix must be square. B=x*y Erorr: ??? Error using ==> mtimes Inner matrix dimensions must agree. A = [1 2 3; 5 1 4; 3 2 1] A = y = A(3,:) y= b = x.* y b= c = x. / y c= d = x.^2 d= x = A(1,:) x= 1 2 3

20 Basic Task: Plot the function sin(x) between 0 ≤ x ≤4π Create an x-array of 100 samples between 0 and 4 π. Calculate sin(.) of the x-array Plot the y-array >>x=linspace(0,4*pi,100); >>y=sin(x); >>plot(y)

21 Display Facilities plot(.) stem(.) Example: >>x=linspace(0,4*pi,100); >>y=sin(x); >>plot(y) >>plot(x,y) Example: >>stem(y) >>stem(x,y)

22 Operators (relational, logical) == Equal to ~= Not equal to < Strictly smaller > Strictly greater <= Smaller than or equal to >= Greater than equal to & And operator | Or operator

23 Flow Control if for while break ….

24 Control Structures If Statement Syntax if (Condition_1) Matlab Commands elseif (Condition_2) Matlab Commands elseif (Condition_3) Matlab Commands else Matlab Commands end Some Dummy Examples if ((a>3) & (b==5)) Some Matlab Commands; end if (a<3) Some Matlab Commands; elseif (b~=5) Some Matlab Commands; end if (a<3) Some Matlab Commands; else Some Matlab Commands; end

25 Control Structures For loop syntax for i=Index_Array Matlab Commands end Some Dummy Examples for i=1:100 Some Matlab Commands; end for j=1:3:200 Some Matlab Commands; end for m=13:-0.2:-21 Some Matlab Commands; end for k=[ ] Some Matlab Commands; end

26 Control Structures While Loop Syntax while (condition) Matlab Commands end Dummy Example while ((a>3) & (b==5)) Some Matlab Commands; end

27 Use of M-File Click to create a new M-File Extension “.m” A text file containing script or function or program to run

28 Use of M-File If you include “;” at the end of each statement, result will not be shown immediately Save file as Denem430.m

29 Notes: “%” is the neglect sign for Matlab (equaivalent of “//” in C). Anything after it on the same line is neglected by Matlab compiler. Sometimes slowing down the execution is done deliberately for observation purposes. You can use the command “pause” for this purpose pause %wait until any key pause(3) %wait 3 seconds

30 Programming tips and tricks Programming style has huge influence on program speed! tic; X=-250:0.1:250; for ii=1:length(x) if x(ii)>=0, s(ii)=sqrt(x(ii)); else s(ii)=0; end; toc tic; X=-250:0.1:250; for ii=1:length(x) if x(ii)>=0, s(ii)=sqrt(x(ii)); else s(ii)=0; end; toc tic x=-250:0.1:250; s=sqrt(x); s(x<0)=0; toc; tic x=-250:0.1:250; s=sqrt(x); s(x<0)=0; toc; slow.m fast.m Loops are slow: Replace loops by vector operations! Memory allocation takes a lot of time: Pre-allocate memory! Use profile to find code bottlenecks!

31.m files.m files are just text files Do work in.m file Paste work into Matlab prompt Use ; to end lines Save.m files Use % to add comments

32 Basic Operations Always use brackets [ ] to define matrices Always use prentices ( ) to call values of matrices The row is always first, the column is always second, i.e. M1(3,2) is not the same as M1(2,3) To see which variables exist, use >>whos To delete variables, use >>clear x y To find out size use >>size(M1)

33 Strengths of MATLAB MATLAB is relatively easy to learn MATLAB code is optimized to be relatively quick when performing matrix operations MATLAB may behave like a calculator or as a programming language MATLAB is interpreted, errors are easier to fix Although primarily procedural, MATLAB does have some object-oriented elements

34 Weaknesses of MATLAB MATLAB is NOT a general purpose programming language MATLAB is an interpreted language (making it for the most part slower than a compiled language such as C++) MATLAB is designed for scientific computation and is not suitable for some things (such as parsing text)

35 References Mastering MATLAB 7. Duane C. Hanselman, Bruce L. Littlefield. Prentice Hall, 2004.Duane C. HanselmanBruce L. Littlefield MATLAB: An Introduction with Applications. Amos Gilat. Wiley, 2003.Amos Gilat