## WeBWorK Problems

### bug in math objects?

by Peter Selinger -
Number of replies: 3
I am looking at this problem: Library/FortLewis/Calc3/17-2-Motion-velocity/HGM4-17-2-30-Motion-velocity-acceleration.pg

For example, with random seed 0, the "correct answer" is displayed as:

i + 4k + (t-2) \cdot 3.14159j + 2k

However, it should be:

i + 4k + (t-2) \cdot (3.14159j + 2k)
+4k+(t2)(3.14159j+2k)
It is not a bug in the problem itself: the code says

$P =$displacement->eval(t=>"$b");$V = $velocity;$T = Formula("(t - $b)") -> reduce;$L = $P +$T * $V; However, the "$V" part of the formula is somehow not correctly parenthesized when displayed by WebWork. The formula is internally treated correctly, i.e., i + 4k + (t-2) (pi j + 2k) is accepted as the correct answer. It just seems to be a display error. Potentially a bug?

-- Peter

### Re: bug in math objects?

by Peter Selinger -
Sorry about the messed-up formatting. There are some characters that are invisible in the HTML editor but show up in ASCII.

The correct answer was displayed as

i + 4k + (t-2) \cdot 3.14159j + 2k

but actually should be

i + 4k + (t-2) \cdot (3.14159j + 2k),

with a parenthesis around the last part.

### Re: bug in math objects?

by Peter Selinger -
I am having a second technical problem with this very question, i.e., Library/FortLewis/Calc3/17-2-Motion-velocity/HGM4-17-2-30-Motion-velocity-acceleration.pg

A student entered the following answer in field 3:

<-3.14sin(3.41t), 3,14cos(3.14t), 5>

Note that he used a comma instead of a period in one of the 3.14's.

Instead of giving a sensible error message, such as "your vector has 4 components", or even a syntax error, his input essentially crashed Perl, and he received the following internal error message:

"Warning -- there may be something wrong with this question. Please inform your instructor including the warning messages below."

and:

WeBWorK Warnings

WeBWorK has encountered warnings while processing your request. If this occured when viewing a problem, it was likely caused by an error or ambiguity in that problem. Otherwise, it may indicate a problem with the WeBWorK system itself. If you are a student, report these warnings to your professor to have them corrected. If you are a professor, please consult the warning output below for more information.
Warning messages

Method 'ijk' can only be used on vectors in three-space at line 565 of [PG]/lib/AnswerHash.pm
Died within AnswerEvaluator::evaluate called at line 1 of (eval 1119)

Answer evaluators must return a hash or an AnswerHash type, not type || at /opt/webwork/pg/lib/WeBWorK/PG/Translator.pm line 1247
Use of uninitialized value in addition (+) at (eval 1031) line 1705.

(End of error message).

I understand that such error messages are usually meant for programming errors, and not in response to wrong user input?

If this is a bug in the problem, I wonder how it could be fixed?

Thanks, -- Peter