# IntervalEvaluators

## Interval Answer Checkers: PG Code Snippet

This code snippet shows the essential PG code to check intervals as student answers. Note that these are insertions, not a complete PG file. This code will have to be incorporated into the problem file on which you are working.

PG problem file Explanation
```  Context("Interval");
# to allow open or closed intervals, uncomment
#    the following line.
# Context()->flags->set(ignoreEndpointTypes=>1);

\$int = Compute("(1,3)");
```

No changes are necessary in the tagging and description and initialization sections of the question file. In the problem set-up section of the file, we set the Context to be the Interval Context.

Once we're in the Interval context, we can define intervals as we'd expect: as shown here, or with limits at infinity:

```  \$int2 = Compute("(-inf,1]");
```

Would give the interval from negative infinity to 1, including the point at one. Note the Context flag to make endpoint checking "fuzzy."

```  BEGIN_TEXT
On what interval is the parabola
\( y = (1-x)(x-3) \)
above the \(x\)-axis?
\$BR
For \(x\) in \{ ans_rule(15) \}
END_TEXT
```

In the text section of the file, we ask the question as usual.

```  ANS( \$int->cmp() );
```

And in the answer and solution section of the file, we can check the answer using our interval MathObject.