fb_unit - mkraska/meclib GitHub Wiki

Feedback function for units input.

This function performs the following checks with units (see fb_vars and fb_number for other functions):

  • Do the units match? This is redundant to the UnitsRelative answer test.
  • Is the value off by exactly an integer power of 10? This indicates correct mantissa and problems with unit conversion. Mantissa Check
  • Is the sign correct? Check of Sign
  • If tol is 0 or the deviation is less than tol: display % deviation with one decimal place.
  • If teacher's answer is zero and student's answer is not: Absolute value of the response is too big.
  • If student's answer is zero and teacher's answer is not: Absolute value of the response is too small.
  • Otherwise display % deviation with one significant digit (e.g. at least 0.01% or 0.3% or 30% deviation)

You can try the function interactively in our Demo Moodle Course (see quiz fb_unit() interactive tryout).

fb_unit(sans, tans, tol) Returns the text to be displayed for feedback.

fb_unitOK(sans, tans, tol) Returns the test result (true or false).

  • sans student's answer,
  • tans teacher's answer,
  • tol relative tolerance for the mantissa. Set it to zero to avoid the tests and just display the deviation.

Question variables

German/English version:

stack_include("https://raw.githubusercontent.com/mkraska/meclib/main/Maxima/fb_value.mac");

Question Text

The question text must contain a [lang ](/mkraska/meclib/wiki/lang-) block to activate localization in the feedback functions.

[lang code="de"](/mkraska/meclib/wiki/lang-code="de") [/lang](/mkraska/meclib/wiki//lang)
[lang code="other"](/mkraska/meclib/wiki/lang-code="other") [/lang](/mkraska/meclib/wiki//lang)

PRT

  • Set simp to false. This enables input like 0*kg to keep the unit factor for feedback.
  • Use a UnitRelative answer test with suppressed feedback (unit mismatch is handled by the feedback function).

Put this to the feedback text of the false branch of the first node.

{@fb_unit(sans, tans, tol)@}

In the true branch of the first node, use this to suppress the tests and just display the deviation:

{@fb_unit(sans, tans, 0)@}

You could pre-calculate the value in the feedback variables, but that doesn not reliably avoid empty checks (with no feedback)