MATLAB: How to call an external function in Cody Coursework

codycourseworkfiles referencedfunction call

I am developing an assignment for my students in Cody Coursework.

I would like them to implement a function "f" that calls another function "g" given by me. The code for "f" would be

function [value] = f(a, b)
  ...
  % Call g
  g(a, b)
  ...
end

I want Cody Coursework to have access to the implementation of "g" and use it in function "f" when called.

Best Answer

You can implement this function g() in a file, say, g.m and upload it in "Files Referenced" when creating a problem within the assignment.

Related Solutions

MATLAB: How to debug Test Suites in Cody Coursework

Remember, the Test Suite is a MATLAB script which, in turn, calls and/or parses the students' code function. So my first recommendation is to use MATLAB on your desktop to build, debug and test your script.

Online, you can also use "Run Tests" during problem creation. Command output is echoed, thus you can print diagnostic data if desired. You can also experiment with MATLAB commands such as dir(), path(), which() etc. as needed.

As a last resort, the host system within which your Test Suite and students' function MATLAB code is executed runs linux. You can use the MATLAB shell escape (!, exclamation point) to execute any needed server-side shell commands. For example, !ls will list all files in the current working directory.

There are many possibilities the power of the MATLAB language offers for implementing test suites. We will add more information and examples in future, and I encourage you to share your own insights as answers or comments below.

MATLAB: How to write an effective Test Suite in Cody Coursework

First, we need to understand why MathWorks has made the Test Suite visible to students. Students are encouraged to use MATLAB on their computer to solve problems. To make this possible, students must be able to copy and paste the Test Suite code into a MATLAB script which, in turn, calls their solution function. Once satisfied, they then copy their solution function into Cody Coursework for assessment.

With this in mind, consider how a student might "game the system" presented with the following Test Suite from the Times2 problem on Cody:

   assert(isequal(times2(1),2));
   assert(isequal(times2(11),22));
   assert(isequal(times2(-3),-6));
   assert(isequal(times2(29),58));

Here, the Test Suite simply calls the students' function, times2, using explicit data values to confirm the students' code returns the expected result. This approach is morally hazardous, as a student can simply write a case or series of if statements to compromise the approach.

Each Test Suite is a MATLAB script. Here we draw on this power to more effectively assess students' code in response to the Times2 problem,

   X=rand(1);
   Y_answer = x*2;
   assert(times2(x),Y_answer)

This still poses two issues, 1. it reveals the answer the students' code needs to implement (i.e. return x * 2), and 2. it does not apply well to complex programming problems.

Now that we've examined what not to do, let's discuss a more effective approach for assessing students' MATLAB code. Faculty already have a reference solution to each programming problem assigned, traditionally offered to teaching assistant staff for manual grading. Protected MATLAB code offers the key of how we use these reference solutions as part of a generalized recipe to write an effective Test Suite.

First, compile your reference solution as Protected MATLAB code.

Second, post this .p file somewhere online accessible by Cody Coursework. This must not be behind the school's firewall, it must be publicly accessible. One option is to use the public folder of a free dropbox account. If using DropBox, it will help to " copy the public link " using their web interface.

Third, implement a test case of your test suite to use your protected reference solution code, for example:

   %%Test Functional Correctness of Students’ Code
   urlwrite('http://url/ProfsFunction.p','./ProfsFunction.p');
   addpath('.');
 
   for i=1:10
     data_vector=rand(1000,1);
     prof_answer = ProfsFunction(data_vector);
     student_answer = StudentsFunction(data_vector);
     assert(isequal(prof_answer,student_answer), 'student code gave an incorrect answer');  
   end

Adapting this for more complex problems will require you adapt the data_vector randomization to something appropriate for your subject matter. Alternatively, you might wish to incorporate a data file from which your Test Suite randomly selects input/output values.

Fourth, add a test case to prevent student attempts to call on the .p file themselves, for example by parsing the students' solution file directly,

   %%Test for attempts to cheat
   found = 0;
   fid = fopen('StudentsFunction.m');
   while(~feof(fid))
      s = fgetl(fid);
      k = regexp(s,'urlwrite\(|ftp\(|mget\(|web\(|fprintf\(|fwrite\(|sprintf\(');
      if ~isempty(k)
          found = 1;
      end
   end
   fclose(fid);
   assert(isequal(found,0))

Fifth, use the solution map as a "line of last defense." Typically, honest solutions which are correct follow similar patterns. Horizontal bars of these patterns form on the solution map. The few stray solutions below these bars which Cody Coursework has marked correct merit manual code inspection.

Best Answer

Related Solutions

MATLAB: How to debug Test Suites in Cody Coursework

MATLAB: How to write an effective Test Suite in Cody Coursework

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