Skip to main content

Grading functions

WirisQuizzes provides a wide range of options for comparing the student's answer to the correct answer when you edit a question. These involve decimal digits, units, simplification, etc. (everything in the Validation options section). However, sometimes we will find that it's necessary to create our own rule for determining when an answer is correct. This can be done via grading functions. A grading function is a user-defined formula that takes the student's response and decides whether it is accurate or not. This allows for even more specificity than the Validation options section options.

Basic grading function

Let's suppose that we want to ask the question "Give a prime number". For this, we need to use a grading function.

First, let's create the grading function. This is done in the Define random variables and functions section. In this example, the grading function will be called gfgf.

programming.gf_prime.calc.png

The function we've defined, gf(x)gf(x), returns true if xx is prime and false otherwise. Select Custom grading function in the Validation options section to use this as the validation method. Then, use the name of the grading function in the blank, in this case, "gf".

gf_ex1.2.png

As for the Correct answer blank, anything will work. Since we've selected Custom grading function as the validation method, the output of the grading function is the only thing that determines correct answers. In this case, we could input a prime number, for example.

Custom marks

We'll show a simple example of a grading function with several outputs. The idea will be to award more marks for every level of correctness in the answer.

We want to ask the following question in basic arithmetic:

gf_ex2.1.png

With partial credit awarded for each correct property of the student's answer. Say these are young children, and we consider the most challenging part to correctly give a number whose remainder is 2 when divided by 7. We'll award 0.4 marks for that and 0.3 for each of the other properties. Additionally, we only want to give half marks for the rest of the properties if the answer falls in the first one (the purpose of decrease_mark).

programming.gf_custom.calc.png

Observe that to make a more extended grading function with multiple conditionals and calculations; we must enclose it with the begin..end statements and use return to define the function's output.

The question is completed now. Make sure to tick the "grading function" option in the Validation options section as described earlier, and give any particular correct value in the Correct Answer blank. We can see that both of these responses are correct:

gf_ex2.3.png
gf_ex2.4.png

We've used a relatively simple question as an example, but we can already see that grading functions can be made to have a very customized and complex design.

Compound answers

We can also create grading functions in the case of compound answer questions. All we need to do is use a separate argument for each answer blank. So, if there are three blanks to fill in, the grading function should look like gf(x,y,z). The first argument corresponds to the first blank, and the second argument corresponds to the second blank, etc. Let's see a simple example.

The question will be a standard exercise in introductory calculus:

gf_ex3.1.png

For this, the following grading function could be used:

programming.gf_compound.calc.png

As opposed to ordinary compound answers, the advantage, in this case, is that we don't need to worry about the order in which the student answers. It also allows virtually infinite answers (here, any solution of the form 8k+18k+1 with kk an integer was valid). However, much more complex behaviour can be programmed, as is easily readily

Empty answer from the student

Imagine that we are working with a compound answer like in the previous example. The student might leave a box empty and just answer some questions, which could crash the validation algorithm, resulting in all grades being 0 even if some were correct.

If you want to grade the answers he had submitted, you need to modify the algorithm and test that all boxes are not empty with the command not_null?. For instance, following the same example above, the algorithm should be as follows.

programming.gf_empty.calc.png

Tip

The not_null? is a precaution you need to use if you want to do something complex with your answer that might crash the program if the response were null. If you are making simple comparisons, you technically don't need it, but we strongly recommend systematically including it to avoid undesired situations.

Answering vectors

It's essential to read this section if you wish to create questions involving vectors. The critical point is that vectors are passed to the grading function as matrices, so we need to de-index them inside the function body to do normal vector operations with them. This should all be clear with the following basic example.

What this all essentially means is that if we pass [...] to a grading function, it will be taken as [ [...] ] (a list with the original vector as its only element). As a result, we cannot do vector operations with it. For example, the vector

gf_vector_ex1.1_calcme.png

will be converted to

gf_vector_ex1.2_calcme.png

How do we access the original vector? It is the first (and only) element of a list, so as with any list, we may access the first element with the subindex "1", as so:

gf_vector_ex1.3_calcme.png

So if "v" was the original vector given by the student and passed to the grading function, to treat it as a vector, we simply need to write "v1" wherever we would like to use "v". Let's look at this with some examples.

Example 1

gf_ex_4.1.png

The matrix has rank 2, so there will be infinite solutions, meaning that we have to use a grading function if we want to allow any possible solution. The procedure itself is pretty simple, but observe that we used the subindex as described above:

programming.gf_vector1.calc.png

The other case we need to cover is allowing students to answer with a row or column vectors (until now, we've only assumed row vectors). We'll illustrate what needs to be done with an example. Using the same question as before, let's say the student responds like so:

gf_vector_ex_2.3.png

This is a column vector, and it is treated differently. All we need to do, though, is transpose it, and we are back to the previous case. We most likely want to allow both types of answers, so at the beginning of the original grading function, we might add the following:

programming.gf_vector2.calc.png

We've added an if statement that simply detects if the input is a column vector (by seeing if the number of columns is 1) and transposes it in that case. If not, then nothing is done to "v". The result is that in all circumstances ", v" will be of the form [ [...] ], and after that, we can use subindices precisely as described previously.

Example 2

Imagine we want to ask the students the following question:

gf_vector_example2_statement.png

This example clearly needs a grading function since there are infinite correct answers.

The first answer is a point, and we only need to check whether it belongs to the corresponding line or not. The first part of the grading function would be

programming.gf_vector_example2.gf1.calc.png

The second answer is a vector, but it is understood as a matrix as before. Similarly, we have to access its first row with a grading function as the following:

programming.gf_vector_example2.algorithm.calc.png

Student's answers to the same question

Another feature approach is using the student's answer in a later part of the question. For instance, imagine you want to ask the following question:

st_ans_ex3.1.png

If a student gets the original line wrong, you may be interested in providing a partial grade if he uses the wrong answer correctly to get the perpendicular gradient. To do so, you need to create a grading function. The CalcMe algorithm must be something as follows:

calc.student_answer2.calc.png

Thus, perpendicular lines passing through the corresponding point will be accepted even though the original line didn't match the initial requirements.

st_ans_ex3.3.png

Keep arguments unevaluated

Suppose that, given an irreducible fraction, we want the student to answer with an equivalent fraction. We will also need a grading function to create this kind of question.

In this case, since we want the student's answer to be interpreted as written, we may select Keep arguments unevaluated , so the evaluation system considers the fraction without simplifying. For instance, if we don't choose this option, it will understand 621 as 27.

gf_arguments_1.png

The corresponding grading function will be called gf . It will give the full grade if the student answers with a fraction mathematically equal to the statement's one, f, and their denominators are different.

programming.gf_arguments.calc.png

Tip

Notice that you have to access to the denominator by x2 instead of through the function denominator(x). It's very important to keep this notation in your mind.

Thus, we will be able to answer with any equivalent fraction, and it will be accepted as correct.

gf_arguments_4.png