Disabling Functions in Student Answers

This shows how to disable functions allowed in student answers.

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Complete Code

Download file: DisableFunctions.pg

PG problem file

Explanation

DOCUMENT();
loadMacros('PGstandard.pl', 'PGML.pl', 'PGcourse.pl');

Preamble

These standard macros need to be loaded. 
# To disable specific operations in student answers, use the undefine
# method for the operations:
Context()->operators->undefine("^", "**");

# We can similarly disable specific functions with the following
Context()->functions->undefine("sin", "cos", "tan", "sqrt");

$ans = Compute("1/2");

# To disallow absolute value, disable abs(),
# sqrt and exponentiation (for sqrt(x^2) and (x^4)^(1/4)), and
# the parentheses | |, and give consistent
# error messages
Context()->functions->disable("abs", "sqrt");
Context()->operators->undefine("^", "**");
Context()->parens->remove("|");
Context()->{error}{convert} = sub {
    my $message = shift;
    $message =~ s/Unexpected character '~~|'/Absolute value is not allowed/;
    return $message;
};

Setup

We can disable specific operations in the Context: in general, predefined operations are * / + - ! >< U ^ ** . ,, for multiplication, division, addition, subtraction, the factorial operation, the cross-product ><, set union, exponentiation (both ^ and ** give exponentiation), the dot product, and list creation (,). `After disabling the operation, they can be re-enabled withoperators->redefine(), e.g.,Context()->operators->redefine(“^”). We can also remove operators withoperators->remove()`, but this is not recommended, as it makes it completely unknown in the Context so that students won’t get helpful error messages if they try to use them.

To disable specific functions in the Context, we similarly undefine them from the predefined functions. The predefined functions are sin, cos, tan, sec, csc, cot, asin, acos, atan, asec, acsc, acot, sinh, cosh, tanh, sech, csch, coth, asinh, acosh, atanh, asech, csch, acoth, ln, log, log10, exp, sqrt, abs, int, sgn, atan2, norm, unit, arg, mod, Re, Im, conj.

In addition, classes of functions can be disabled with functions->disable():

  • Context()->functions->disable("Trig"); (disables all trig functions in both SimpleTrig and InverseTrig functions)
  • Context()->functions->disable("SimpleTrig"); (disables sin, cos, tan, sec, csc, cot)
  • Context()->functions->disable("InverseTrig"); (disables asin, acos, atan, asec, acsc, acot, atan2)
  • Context()->functions->disable("Hyperbolic"); (disables all hyperbolic functions in both SimpleHyperbolic and InverseHyperbolic functions)
  • Context()->functions->disable("SimpleHyperbolic"); (disables sinh, cosh, tanh, sech, csch, coth)
  • Context()->functions->disable("InverseHyperbolic"); (disables asinh, acosh, atanh, asech, acsch, acoth)
  • Context()->functions->disable("Numeric"); (disables ln, log, log10, exp, sqrt, abs, int, sgn)
  • Context()->functions->disable("Vector"); (disables norm, unit)
  • Context()->functions->disable("Complex"); (disables arg, mod, Re, Im, conj)
  • Context()->functions->disable("All"); Alternatively, we could use the following syntax.
 Parser::Context::Functions::Disable('All');
BEGIN_PGML
Find the numerical value: [` \sin^2(\pi/4) = `] [____]{$ans}
END_PGML

Statement

This is the problem statement in PGML. 
BEGIN_PGML_SOLUTION
Solution explanation goes here.
END_PGML_SOLUTION

ENDDOCUMENT();

Solution

A solution should be provided here.