Script File Input – Output : Chapter 4

1. MATLAB – More Script Files PLEASE HAVE STUDENTS START MATLAB NOW Script File Input – Output : Chapter 4

2. Introduction • In this lecture we will learn various ways of writing and executing programs in MATLAB. • Techniques will be shown for getting data into and out of programs. • We will be using the calculation of a GPA (Grade Point Average)as an example throughout this lecture. • Notice how appropriate comments in the code help • understand what is being done. You will be asked to add such comments to every script file from now on.

3. Calculating your GPA • Step 1: • Identify the grades for the courses. For example, • ENG 183 - Grade A • MATH 251 - Grade A- • ENG 191 – Grade B • Step 2: • Convert the letter grades into point grades based on OSU system: • Grade A : 4.0 Pts • Grade A- : 3.7 Pts • Grade B+ : 3.3 Pts • Grade B : 3.0 Pts and so on… • Hence: • ENG 183 - 4.0 • MATH 251 - 3.7 • ENG 191 – 3.0

4. Calculating your GPA : contd. • Step 3: • Find the credit hours for each of the courses. • For example: • ENG 183 - 3 Credit Hours - 4.0 Grade • MATH 251 - 5 Credit Hours - 3.7 Grade • ENG 191 - 4 Credit Hours - 3.0 Grade • Step 4: • Calculate your GPA based on the following formula • (Grade in ENG183)*(Credit Hours for ENG183) + (Grade in MATH 251)*(Credit Hours for MATH 251) + (Grade in ENG 191)*(Credit Hours for ENG 191) • Credit Hours for ENG183 + Credit Hours for MATH251 + Credit Hours for ENG191 • = ( (4*3) + (3.7*5) + (3*4) ) / (3+5+4) • = 3.541 GPA =

5. Writing a MATLAB Program for GPA Calculation • Write a MATLAB program for the GPA calculation for the example shown in the previous slide. Use variables so the program can be used for any set of grades/credits. • Steps: • Create variables for the grades as grade1, grade2 etc. • Create variables for the credit hours as credit1, credit2 etc. • Write the formula for the GPA calculation using the above variables • Values are: • Grade1=4 , Grade2=3.7, Grade3=3 • Credit1=3, Credit2=5, Credit3=4 • ENG 183 - 3 Credit Hours - 4.0 Grade • MATH 251 - 5 Credit Hours - 3.7 Grade • ENG 191 - 4 Credit Hours – 3.0 Grade

6. Writing MATLAB Program for GPA Calculation clear % Initialization of variables clc disp(‘Your Name') disp('Seat Number') % Assign the grades for 3 subjects grade1=4; grade2=3.7; grade3=3.0; % Assign the credit hours for the 3 subjects credit1=3; % Now complete the program!! credit2=5; credit3=4; % Calculate the GPA from the equation GPA = ((grade1*credit1)+(grade2*credit2)+ (grade3*credit3)) / (credit1+credit2+credit3)

7. Writing MATLAB Program for GPA Calculation : Using Vectors • Now write a MATLAB program for the GPA calculation using vectors for the grades and credit hours. • Steps: • Create a vector called grade to put the values of grade • Create a vector called credit to put the values of credit hours • Write the formula for the GPA calculation with vectors using element by element arithmetic

8. Writing MATLAB Program for GPA Calculation : Using Vectors clear %Initialization of variables clc disp(Your Name') disp(' ') disp('Seat Number') disp(' ') % Assign the grades for 3 subjects in a vector grade=[4 3.7 3]; % Assign the credit hours for the 3 subjects in a vector % Complete the program!!! credit=[3 5 4]; % Calculate the GPA by doing element by element arithmetic GPA = sum(grade.*credit) ./ sum(credit) Note that we use the vector arithmetic and the sum function to find GPA

9. Data Inputs to Programs • Both of the previous programs defined and assigned values to variables for grade and credit hours inside the program. • If we wish to run these programs for a different set of grades/credits, we have to change the program. • Once a program is written and verified, it is best not to change it. We need a better way to change input data.

10. INPUT TO A SCRIPT FILE • The previous method requires the user to know the names of variables when assigning the values. • Another method is to prompt the user to enter the values. This would make your program more robust and also user-friendly. This is done by using the input() command: x = input('text') Note the use of single quotes

11. Interactive Example For example, create a script file with: x = input('Please enter a value for x: ') Execute the script  The command window asks you: Please enter a value of x: x = 5 5 User Input

12. Interactive Example using vectors Below is shown the program we just discussed treating the grades and credit hours as vectors. clear clc disp('Your name') disp('Seat number') % Ask the user to enter the 3 grades as a vector grade=input('Enter the Grades as a vector :'); % Ask the user to enter the 3 credit hours as a vector credit=input('Enter the corresponding Credit Hours as a vector :'); % Calculate the GPA by doing element by element arithmetic GPA = sum(grade.*credit) ./ sum(credit) Output on next slide

13. Interactive Example using vectors : Output The values in red are entered following the prompt Your name Seat number Enter the Grades as a vector : [4 3.7 3] Enter the corresponding Credit Hours as a vector : [3 5 4] GPA = 3.5417

14. Improving the output: (see Example.m) % Put grades and credit hours together as a table TBL = [credit;grade]; % print headers (can be disp or fprintf) fprintf('\n Grade Summary\n\n') disp(' Credit') disp(' Hours Grade') %body of table fprintf(' %1i %3.1f\n',TBL) %final results fprintf('\n The overall GPA is: %0.2f\n',GPA)

15. Produces Grade Summary Credit Hours Grade 3 4.0 5 3.7 4 3.0 The overall GPA is: 3.54

16. Additional Example Script File clear %Initialization of variables clc disp('Your Name') disp(' ') disp('Seat Number') disp(' ') %script file computes the free-fall velocity of a bungee jumper %t=time (s) %m=mass(kg)of the jumper %cd = second-order drag coefficient(kg/m) %v=downward velocity (m/s) g=9.81; m=68.1; t=12; cd=0.25; v=sqrt(g*m/cd)*tanh(sqrt(g*cd/m)*t)

17. Script Example (Contd.) Command Window Output: Your Name Seat Number v = 50.6175 >>