MATLAB Grader -- assessing functions

Reference Solution:

function results = drinking_age(x)

if x < 0

results = 'Invalid age'

end

if x >= 21

results = 'You are of drinking age'

else

results = 'You are not of drinking age'

end

end

Assessment:

% Run learner solution.

x = 1;

results = drinking_age(x);

% Run reference solution.

yReference = reference.drinking_age(x);

% Compare.

assessVariableEqual('results', yReference);

The assessment claims all is good : x=25 drinking_age(x)

When I change the >= to ==, the assessment says all is good

function results = drinking_age(x)

if x < 0

results = 'Invalid age'

end

if x == 21

results = 'You are of drinking age'

else

results = 'You are not of drinking age'

end

end

Answer 1

[Cris LaPierre]

Perhaps you could explain what it is you think should be happening?

The value of x used to assess the learner solution is defined in your assessment test:

% Run learner solution.

x = 1; %<---------- Defined here

results = drinking_age(x);

% Run reference solution.

yReference = reference.drinking_age(x);

I assume the code 'x=25' has been added to the 'Code to call your function' field. Since functions must be called in order to run, this field just gives learners a way to test their function before submitting. It has nothing to do with assessing the function.

So, in your case, your assessment test is always checking the functions using x=1. Since 1 is much less than 21, it doesn't matter if you use >=21 or ==21. The else case is still the one that executes.

[the cyclist]

I'll just make a side comment here that since you don't return after

if x < 0
    results = 'Invalid age'
end

the code will keep going and also return a result of

results = 'You are not of drinking age'

You may instead want

if x < 0
    results = 'Invalid age'
    return
end

[Nicole]

your assessment test is always checking the functions using x=1

Thank you, I didn't realize that and thought it was just a "starting point" to define the variable.

I thought it was sending/evaulating the x in the 'code to call your function'

This could explain some other issues I was having. I will go back and update other assignments - thanks for the quick response!

[Nicole]

Cris -

Is there a way to assess more than 1 x?

I'd like to test -10 and 30, for example

[Cris LaPierre]

There are 2 possible ways. First is to have the function written in such a way as to accept a vector as input, and return a corresponding output. The second is to test each input separately.

For the function you have shared, I think the easiest is to either create a separate assessment test for each case, or have a single assessment test all three:

% Test 1 
x = 1;
results = drinking_age(x);
yReference = reference.drinking_age(x);
 
% Compare.
assessVariableEqual('results', yReference);

% Test 2 
x = 10;
results = drinking_age(x);
yReference = reference.drinking_age(x);
 
% Compare.
assessVariableEqual('results', yReference);

% Test 3
x = 30;
results = drinking_age(x);
yReference = reference.drinking_age(x);
 
% Compare.
assessVariableEqual('results', yReference);

Ultimately, you are designing a learning experience for your students. What will work best for them? If you split this into 3 separate assessment tests, then you can give partial credit if they get some scenarios working but not others. You can also give more specific feedback related to each individual scenario.

If you put everything into a single test, it may look less intimidating to your learners, but can be harder to help them identify their mistake if they are incorrect.