[LON-CAPA-users] Puzzling situation...

[Stuart Raeburn]

Hi,

> Any ideas anyone on why in the second instance ($db12, id=25) 0 is   
> accepted as a correct answer but in the other instance ($dy11,   
> id=22), 0 is returned as incorrect???

Perhaps you are seeing an artifact of floating point calculations in  
the situation where the answer is zero, and you are using a relative  
tolerance?

Stuart Raeburn
LON-CAPA Academic Consortium


Quoting "Mills, Douglas G" <dmills at illinois.edu>:

> HI All,
>
> We're greatly perplexed by this situation.  We have a student whose   
> results for two different responses in a part should be 0, but the   
> answer is accepted for one of the responses and not accepted for the  
>  other. To the best of my abilities to discern, everything about the  
>  two items is identical (and having written these, it's almost   
> certain that I cut and pasted my way from one to the other) and the   
> data for the two are analogous.
>
> The formulas for computing the two answers are:
>
> $dY11=&format($EAY11-$AY11,"2s");
> $dB12=&format($EAB12-$AB12,"2s");
>
> The values for the variables in her instance are:
>
> $EAY11=4.2e-1
>
> $AY11=.42
>
> $EAB12=2.6e-1
>
> $AB12=.26
>
> The coding in the problems looks (is!?) identical as well:
>
> <numericalresponse format="2f" answer="$dY11" id="22">
> <responseparam name="tol" type="tolerance" default="2%"   
> description="Numerical Tolerance" />
> <responseparam name="sig" type="int_range" default="1,2"   
> description="Significant Digits" />
> <textline /> $PART20msg[1]
> </numericalresponse>
>
> <numericalresponse format="2f" answer="$dB12" id="25">
> <responseparam name="tol" type="tolerance" default="2%"   
> description="Numerical Tolerance" />
> <responseparam name="sig" type="int_range" default="1,2"   
> description="Significant Digits" />
> <textline /> $PART20msg[4]
> </numericalresponse>
>
> Any ideas anyone on why in the second instance ($db12, id=25) 0 is   
> accepted as a correct answer but in the other instance ($dy11,   
> id=22), 0 is returned as incorrect???
>
> Doug
>
> Douglas Mills
> Director of Instructional Technologies
> Department of Chemistry
> University of Illinois
> dmills at illinois.edu<mailto:dmills at illinois.edu>
> (217) 244-5739
>