FormattingDecimals
Using Logarithms: PG Code Snippet
We show how to use logarithmic functions in PG problems.
PG problem file | Explanation |
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DOCUMENT(); loadMacros( "PGstandard.pl", "MathObjects.pl" ); TEXT(beginproblem()); |
Initialization: Standard. |
Context("Numeric"); Context()->variables->set(x=>{limits=>[2,4]}); # # both ln and log are natural log (base e) # $a = 6; # or $a = random(3,7,1); # # log base e # $b = sprintf("%0.3f", ln($a) ); # or log($a) $solution1 = Real("$b"); $f = Formula("ln(x)"); # or log(x) $solution2 = $f->eval(x=>$a); # # log base 10 is log10, logten, # ln(x)/ln(10), or log(x)/log(10) # $c = sprintf("%0.3f", ln($a)/ln(10) ); # or log($a)/log(10) $solution3 = Real("$c"); $g = Formula("ln(x)/ln(10)"); # or log(x)/log(10) $solution4 = $g->eval(x=>$a); |
Setup:
Since the domain of a logarithmic function is all positive real numbers, we should set the domain of function evaluation to
Use perl's We used the logarithm change of base formula log_{10}(a) = log(a) / log(10) = ln(a) / ln(10) to get a logarithm base 10.
Note: If we load
It is possible to set a context flag that will use the base 10 log via If you would like to define log base 2 (or another base) see AddingFunctions for how to define and add a new function to the context so that students can enter it in their answers. |
Context()->texStrings; BEGIN_TEXT Notice the formatting and rounding differences between \( $solution1 \) and \( $solution2 \). $BR $BR Try entering \( \ln($a), \log($a), \ln($a)/\ln(10), \log($a)/\log(10), \mathrm{logten}($a), \mathrm{log10}($a) \). $BR $BR \( \ln($a) = \) \{ ans_rule(20) \} $BR \( \ln($a) = \) \{ ans_rule(20) \} $BR \( \log_{10}($a) = \) \{ ans_rule(20) \} $BR \( \log_{10}($a) = \) \{ ans_rule(20) \} END_TEXT Context()->normalStrings; |
Main Text: Notice the difference in decimal formatting when "Show Correct Answers" is checked and you click "Submit Answers". |
ANS( $solution1->cmp() ); ANS( $solution2->cmp() ); ANS( $solution3->cmp() ); ANS( $solution4->cmp() ); ENDDOCUMENT(); |
Answer Evaluation: Standard. |