FormulaTestPoints

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Revision as of 21:46, 14 February 2008

Formula Test Points for Evaluation: PG Code Snippet

This code snippet shows the essential PG code to specify the points on which a formula is evaluated when a student's answer is checked. 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.

This can, of course, be done with new and old-style answer evaluators. An example of the latter appears below. Also note that we may want to do this in two different ways: either by setting the domain on which the formula is evaluated (that is, the limits of evaluation), or by setting specific test points on which the formula should be considered. These are both shown below.

Problem Techniques Index

PG problem file Explanation
  Context()->variables->set(x=>{limits=>[-1,1]});
  $func = Compute("sqrt(x+1)");

  ## Alternately:
  # Context()->flags->set(limits=>[-1,1]);
  # $func = Compute("sqrt(x+1)");

  ## Or, setting the limits only for the given
  ##    formula, we don't need to reset the Context,
  ##    and just include
  # $func = Compute("sqrt(x+1)");
  # $func->{limits} = [-1,1];

  $gunc = Compute("sqrt(x^2 - 4)");
  $gunc->{test_points} = [[-3],[-2],[2],[3],[4]];

We don't have to change anything in the documentation and tagging or initialization sections of the PG file. In the problem set-up, we can specify the limits on which all Formulas are evaluated by setting the limits for the variable in the problem (in this case, x) in the Context. Alternately, we can set the Context flag limits to set the limits on all variables in the Context, as shown in the commented-out line, or can set the limits for the formula itself, as in the second commented-out line. (Obviously, only one of these three is needed.)

It is also possible to specify the actual points on which the Formula will be evaluated. This is an attribute of the Formula itself; the call is shown for our formula $gunc. In this case there is only one variable, so we have only to specify a single value for each point where the function is to be evaluated. If the function were a function of two variables, then we might use something like $formula->{test_points} = [[-3,-2],[-2,0],[2,0],[3,2],[4,5]]. Note that the test points are given in alphabetical order! Thus, if the variables in the formula are specified as x and C, the test point [3,2] is C=3 and x=2.

One final note: if the formula is a function of more than one variable and we're specifying limits in the formula, we need to specify the limits for all variables. Thus, we'd have something like $formula->{limits} = [[-1,1],[0,2]]. Again, the limits are specified for each variable in alphabetical order.

  BEGIN_TEXT
  Enter \( $func \): \{ ans_rule(35) \}
  $BR
  Enter \( $gunc \): \{ ans_rule(35) \}
  END_TEXT

The text portion of the file is the same as usual.

  ANS( $func->cmp() );
  ANS( $gunc->cmp() );

And the answer evaluation is as we'd expect.

With old-style answer evaluators, we can do the same thing:

PG problem file Explanation
  $func = "sqrt(x+1)";
  $gunc = "sqrt(x^2 - 4)";

We define the functions as expected in the problem set-up section of the file.

  BEGIN_TEXT
  Enter \( \sqrt{x+1} \): \{ ans_rule(35) \}
  $BR
  Enter \( \sqrt{x^2 - 4} \): 
  \{ ans_rule(35) \}
  END_TEXT

And the text portion of the file is similarly mundane.

  ANS(fun_cmp($func, limits=>[-1,1]));
  ANS(fun_cmp($gunc, test_points=>[-3,-2,2,3,4]));

The limits or test points are specified in the fun_cmp call. Note that we can use the short-hand [-3,-2,2,3,4] for the list of points when there is only one variable; in the case of multiple variables, we would have to specify a list of lists as we did above.

Problem Techniques Index

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