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Introduction to MATLAB

Introduction to MATLAB. Programming with MATLAB 1. 1 Applied Numerical Methods with MATLAB for Engineers and Scientists , 2nd ed., Steven C. Chapra, McGraw Hill, 2008, Ch. 3. Outline. M-files Script files* Function files Interactive Input and output Enter information Display result

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Introduction to MATLAB

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  1. Introduction to MATLAB Programming with MATLAB1 1Applied Numerical Methods with MATLAB for Engineers and Scientists, 2nd ed., Steven C. Chapra, McGraw Hill, 2008, Ch. 3.

  2. Outline • M-files • Script files* • Function files • Interactive Input and output • Enter information • Display result • Structured programming • Decisions (or Selection) • Loops (or Repetition)

  3. M-files • M-files: An M-file is a text file stored with a .m extension. • To create a new M-file: Go to File, New, M-file. • Type in the commands line by line in the edit window. • Save the file as filename.m. • To execute an M-file: Type the filename without .m in the command window. • Two types of M-files: • Script files: A script file is a set of MATLAB commands that are saved on a file – we consider script files mainly in this course. • Function files: Read 3.1.2 and 3.5 of the hand-out.

  4. Example: bungee-jumper-1.m • Develop a script file to compute and plot the velocity v of the bungee jumper as a function of time t. Set t = 0 to 20 s in steps of 2. • Save it as bungee-jumper-1.m • Execute the file. • What are the values of v at t = 0, 10, and 20 s? t=[0:2:20]’; %Time(s) g=9.81; %Acceleration due to gravity(m/s^2) m=68.1; %Mass (kg) cd=0.25; %Drag coefficient (kg/m) v=sqrt(g*m/cd)*tanh(sqrt(g*cd/m)*t); figure; %To open a figure window plot(t, v) title(‘Plot of v versus t’) xlabel(‘Values of t’) ylabel(‘Values of v’)

  5. Interactive Input and output • The input command: n = input('promptstring’):Prompt the user to enter a value from the keyboard n = input('promptstring','s'): Prompt the user to enter a string from the keyboard • Examples: >> m = input(‘Mass (kg): ‘); >> myname = input(‘My name is: ‘,’s’);  • The display command: display(value): value = a numeric value, a variable, or a string enclosed in ‘ ‘. • Examples: >> display(m) >> display(myname)

  6. Example: bungee-jumper-2.m g=9.81; %Acceleration due to gravity(m/s^2) m=input(‘Mass (kg): ‘); cd=input(‘Drag coefficient (kg/m): ‘); t=input (‘Time (s): ‘); v=sqrt(g*m/cd)*tanh(sqrt(g*cd/m)*t); disp(‘ ‘) disp(‘Velocity (m/s):’) disp(v) • In the bungee-jumper example, create a script file that prompts the user to enter the values for the mass, m, in kg, the drag coefficient, cd, in kg/m, and the time, t, in s. Also, compute and display the value for the velocity, v, at the specified time instant. • Save the file as bungee-jumper-2.m. • Run the file.

  7. Input: grade = numerical value (0 -100) grade >= 60 F T Output: displayed message (‘passing grade’) Structured programming: Decisions (1) The if Structure: • Syntax: if condition statements end • Example: Write an M-file (Grade.m) to evaluate whether a grade is passing. See the flowchart.

  8. Input: grade = numerical value (0 -100) grade >= 60 T F Output: displayed message (‘Not passing grade’) Output: displayed message (‘passing grade’) Structured programming: Decisions (cont.) (2) The if…else Structure: • Syntax: if condition statements1 else statements2 end • Example: Modify Grade.m to evaluate whether a grade is passing or not passing. See the flowchart.

  9. Structured programming: Decisions (cont.) (3) The if…elseif Structure: • Syntax if condition1 statements1 elseif condition2 statements2 . . . else statementselse end • Example: Write an M-file (mysign.m) to do the following: Input x; If x > 0, display ‘sign = 1’; if x < 0, display ‘sign = -1’; otherwise, display ‘sign = 0’.

  10. Relational operators in MATLAB

  11. Logical operators in MATLAB Priority of the operators: Highest Lowest

  12. Structured programming: Loops (1) The for…end Structure: • Syntax: for index = start:step:finish statements end • Note: • If an increment of 1 is desired, the step can be dropped. • step can be any numeric value, integer or non-integer, positive or negative. • Example: Write your own M-file (mysum.m) to compute the following sum using a for loop: 1 + 2 + 3 +…100 Also, check the MATLAB built-in function sum.

  13. Structured programming: Loops (cont.) (2) The whilestructure: A while loop repeats as long as a logical condition is true. • Syntax: while condition statements end • Example: What will be displayed? x = 8 while x > 0 x = x – 3; disp(x) end

  14. Structured programming: Loops (cont.) (3) The while…break loop: It allows loop termination on a true condition anywhere in the loop. • Syntax: while (1) statements if condition, break, end statements end • Example: What will be the final x value? x = 8; while (1) x = x – 5; if x < 0, break, end end

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