1. EK 127 Homework 2: Grading Script Parser
Background
In most every lab section, you have some problems you are required to submit on Edge. The
code you submit on Edge is typically a script that accomplishes some desired task, and the
online platform automatically grades it and provides feedback.
The embedded MATLAB on Edge works in a fairly unique way. MATLAB is by no means built into
your browser. What happens is your code is sent as a string to a MathWorks server where it is
evaluated (as in the eval function is used), and the results are sent back to you on Edge.
For clarity, we will refer to the student answer (the actual code you type into Edge) as the
“answer code”. Additionally, the code that automatically grades the answer code will be
referred to as the “grading code”.
Immediately after the answer code, the grading code is also processed by a MathWorks server.
Since both scripts are run in the same workspace, any variable created in the answer code are
accessible in the grading code.
Just as you write the answer code, someone had to have written the grading code, right? The
grading code accomplishes a variety of tasks, such as making sure a certain function is used,
making sure the answer is correct, making sure a loop is or isn’t used, etc.
Sometimes, it is very useful to process the answer code as a text file. If the answer code is seen
as just text, we can use our string manipulation functions on it. As an example, one common
task is to remove all comments from the answer code.
Assignment
Your task is to write a portion of the grading code to grade Problem 3.4 from Worksheet 3
(which was to write the diff function). Your code needs to do the following:
• Read the answer code as a text file
• Delete OR ignore all comments
• Check to see if the answer code uses the subtraction operator (the minus sign)
• If the answer code does NOT use the subtraction operator, assert an error and provide
feedback using the assert function
• Check to see if the answer code uses the diff function
• If the answer code DOES use the diff function, assert an error and provide feedback
using the assert function

2. The assert function is a built-in function that generates an error when a condition is violated.
For example:
assert(isequal(myprod,myprod_test),'Check your expression for myprod')
Here, myprod is the student’s answer and myprod_test is the correct answer to check it against.
This statement checks to see if the variables myprod and myprod_test hold the same value. If
they do (so the condition is true), nothing happens. If the values are different (so the condition
is false), it asserts an error and provides a feedback statement of “Check your expression for
myprod”.
In addition to the assert function, you will need to use some string functions. Please refer to
your book, notes, and online resources to find helpful functions.
Additional Guidance
To understand the nature of the problem even better, you should play around with this
problem on Edge (see: Week 3, WS3 Edge Submit Problems, the 4th
problem titled
“Difference”). Try to make intentional mistakes and see what happens! For instance, what
happens if you use the diff function? What if the word “diff” is used in a comment? Playing
around with it on Edge should help you out with writing your solution.
Some sample M-files have been provided as well. These should help you test your solution (you
can find these on Edge):
1. correct_answer.m - A perfect, vectorized solution
2. uses_diff.m - A correct solution that uses the diff function
3. incorrect_answer.m - An incorrect solution that attempts to use a for loop
4. assert_sample.m - A quick example of how the assert function is used
Note: Both examples 1 and 2 contain “diff” in a comment.
You may also find the following useful:
1. fileread() - a function useful for reading the entire file as a string
2. char(10) - the newline character that separates each line in the file. Comments will
always be on separate lines from actual code to making parsing out/ignoring comments
easier.