AddingFunctions
Adding Functions to the Context: PG Code Snippet
This code snippet shows the essential PG code to add a named function to the Context in a problem. (March 2010: There is a easier way to do this: parserFunction.pl.html.) 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. (The information here is taken from this discussion thread and a sample problem in the doc/parser/extensions directory of the WeBWorK tree.)
Example 1: The newer and easier way to add a function to the context.
| PG problem file | Explanation |
|---|---|
loadMacros(
"MathObjects.pl",
"parserFunction.pl",
);
parserFunction("f(x,y)" => "sqrt(x*y)");
|
Initializaiton and Setup:
We need to load the |
Example 2: The rudimentary way to add a function to the context.
| PG problem file | Explanation |
|---|---|
package NewFunc;
# this next line makes the function a
# function from reals to reals
our @ISA = qw(Parser::Function::numeric);
sub log2 {
shift; my $x = shift;
return CORE::log($x)/CORE::log(2);
}
package main;
# Make it work on formulas as well as numbers
sub log2 {Parser::Function->call('log2',@_)}
# Add the new functions to the Context
Context()->functions->add(
log2 => {class => 'NewFunc',
TeX => '\log_2'}, );
|
To define our new function, we first create a class in which it can live, where the behavior of the function is articulated, and then we add the function to the Context for the problem. Here, we borrow from the extensions sample provided in the webwork2/doc directory of the distribution and define a log base 2 function. If we didn't have any fancy TeX formatting for the function we could omit that hash key in the functions->add() call from the Context.
We can define a multivariable function by changing the inheritance list: if we had
sub f {
shift; my ( $x, $y ) = @_;
...
}
|
BEGIN_TEXT
Solve \( 2^{3x} = 5 \):
\( x = \) \{ ans_rule(25) \}
$BR
${BITALIC}(Your answer may involve the
function \(log_2(x)\), which you should
enter as ${BTT}log2(x)$ETT.)$EITALIC
END_TEXT
|
The problem text is as we would expect, except that we are allowed to use the function that we defined in the problem text. |
ANS( Compute("(1/3)*log2(5)")->cmp() );
|
And then in the answer and solution section of the problem the function may also be used. |
- POD documentation: parserFunction.pl.html
- PG macro: parserFunction.pl
