Check of Sign

Procedure based on this forum discussion.

This check is implemented in the feedback function fb_unit.

Question variables

ra(x,y):=stack_units_nums(stack_unit_si_to_si_base(x))/stack_units_nums(stack_unit_si_to_si_base(y));

When checking the sign of symbolic expressions, you might want to assume that any variable in the expression is positive.

map(lambda ([x], assume(x>0)),listofvars(expression));

PRT

This example is in the context of a unitless question design but input with units.

Field	Value
Answer test	AlgEquiv
SAns	is(ra(S_A, A)>0) Answer S_A is made unitless by dividing it by the model solution
TAns	true
true feedback	Das Vorzeichen stimmt.