Introduction To Matlab Class 1 Instructors: Hristiyan (Chris) Kourtev and Xiaotao Su, PhD Double click the matlab icon When prompted click “Skip”, then type: mkdir C:/MatlabClass/YourLastName cd C:/MatlabClass/YourLastName

http://ruccs.rutgers.edu/matlab_course/ Introduction Ask Questions! Slides, notes, assignments, and other info will be at: http://ruccs.rutgers.edu/matlab_course/

Setup Click Matlab mkdir C:/MatlabClass/YourLastName cd C:/MatlabClass/YourLastName

Programming Matlab has its own programming language What is a program? A series of instructions that the computer follows Also referred to as “Code” or a “Script”

Two Options For Where To Issue Commands/Instructions In the command window In a script (program) executed by the command window.

Note: The “_” character is the shifted dash SHIFT + - Hello World At the command prompt type: my_var = ‘hello world’; And press ENTER. Note: The “_” character is the shifted dash SHIFT + -

Hello World my_var = ‘hello world’; Semi-colon is so you don’t output the result to the screen. Single quotes denote character string Variable Name

Variables num_oranges = 3.5 num_apples = 7 7 3.5 my_var num_oranges my_var = ‘hello world’; num_oranges = 3.5 num_apples = 7 7 ‘hello world’ 3.5 my_var num_oranges num_apples Variable Name

Memory Your computer’s memory Each of the values are stored in memory associated with the variable name The “who” command will list the current variables in memory Typing my_var will return the value of that variable Var Name Value my_var ‘hello world’ num_apples 7 num_oranges 3.5 subject_name ‘john smith’ …

Setting values As you have seen you set the value of a variable with the “=“ sign You can also set a variable equal to another variable or the output of an operation on a variable.

Setting values new_var = my_var third_character = my_var(3) this is 7 fruit = num_apples + num_oranges this is now 10.5 num_apples = 6 what is the value of fruit now?

Changing around strings my_var is currently ‘hello world’ Typing my_var(3) will return ‘l’ my_var(3) = my_var(1) Now what is the value of my_var?

Calling Functions A function is a program that you call on to do some sort of action length(‘hello world’) length(my_var) disp(my_var)

disp( length(‘hello world’) ) Nesting Functions disp(length(my_var)) What happens here? disp( length(‘hello world’) ) disp(11) 11

Your first program What is pseudo-code and why we need it Typing commands one at a time isn’t very efficient, especially when you want to do the same ones repeatedly… so we create a program to do it This program will be called mix_strings

Comments Comments are descriptions of what is happening in your code. They are need to follow what is happening for debugging purposes At the beginning of a script you put in a type of comment called a header

% symbol makes this line “commented out” This means that the computer will ignore these lines These lines aren’t for the computer, they are for you % mix_strings.m % % Displays the string ‘hello world’ % Then scrambles letters in that string and % displays the scrambled string % written by XYZ 3/6/2005 Name of file Description: What does this file do? Who wrote it and when?

So what is the header good for? Save the file At the command line type: help mix_strings All matlab programs have headers. Find out information on disp, pause, and length

What else? lookfor can be used to search for programs that have certain words in their headers. lookfor string lookfor random

Back to the program clear all; my_var = ‘hello world’; mixstr = my_var; mixstr(3) = my_var(1); mixstr(1) = my_var(3); disp(mixstr);

Now run it In the command window: mix_strings

loops for i=1:5 disp(i) end; Used to repeat the same chunk of code many times for i=1:5 disp(i) end;

mix_strings2.m clear all; my_var = ‘hello world’; mixstr = ‘xxxxxxxxxx’; for i=1:length(my_var) mixstr(i) = my_var(i); end; disp(mixstr)

rand and ceil rand will create a random number from 0 to 1 ceil will round up any number to the next integer Together you can create random integers ceil(rand*7)

task 1 Replace each x in mixstr with a random character from my_var. Start with the first x, then the second x… ‘hello world’ ‘xxxxxxxxxxxxx’ Result could be -> ‘wdolhrdlhlwe’

% mix_strings3.m % %Displays the string 'hello world‘, then scrambles letters in that string %and displays the scrambled string % written by Chris Kourtev 7/12/2010 clear all; my_var = 'hello world'; mixstr = 'xxxxxxxxxxxxx'; disp(my_var); for i = 1:length(mixstr) mixstr(i) = my_var(ceil(rand*length(my_var))); end; disp(mixstr);

mat = [1, 5, 3; 2, 1, 5; 7, 9, 0] Vectors & Matrixes A string is a list of characters You can also have lists of numbers using vectors and matrixes vect = [1, 2, 5, 6, 3] mat = [1, 5, 3; 2, 1, 5; 7, 9, 0] mat = [1, 5, 3; 2, 1, 5; 7, 9, 0]

mat = [1, 5, 3; 2, 1, 5; 7, 9, 0] Vectors & Matrixes 1 2 5 6 3 1 5 3 2 vect = [1, 2, 5, 6, 3] mat = [1, 5, 3; 2, 1, 5; 7, 9, 0] mat = [1, 5, 3; 2, 1, 5; 7, 9, 0] 1 2 5 6 3 Vect mat 1 5 3 2 7 9 note: vectors are basically 1 dimensional matrixes

Getting Values out of Vectors & Matrixes 1 2 5 6 3 vect(3) returns 5 mat 1 5 3 2 7 9 mat(3,1) returns 7 Note: to get a cell you use (ROW, COLUMN)

vector as a 1D matrix vect = [1; 2; 3] vect2 = vect’ 1 2 3 1 2 3

transposing mat 1 5 3 2 7 9 1 2 7 5 9 3 mat = if you set t_mat = mat’ if you set t_mat = mat’ t_mat(3, 1) is equal to mat(1,3) Rows and columns are swapped when you transpose a matrix mat’ = 1 2 7 5 9 3

performing operations vect + 3 vect + vect vect - 3 vect + [5, 4, 3] mat+mat’

multiply and divide Don’t forget to put a dot before multiplication and division symbols vect.*3 mat.*0.5 vect./2 vect2 = [2; 2; 4] vect.*vect2 vect./vect2

task 2 Create a 6(rows)x4(columns) matrix filled with random integer values between 1 and 20 Create a zeroes matrix of the same dimensions Replace each zero with a random number from the other matrix (as we did in the mix_strings program) Display each value in the new mixed matrix Hint 1: You will need to use nested loops Hint 2: Look up how to use the “zeros” command ** Advanced task: Design your program so that it can work with matrices of any dimension just by changing the number of rows and column. Hint: Look up the “size” command