## WeBWorK Problems

### Re: Math Objects and multi answer

by Davide Cervone -
Number of replies: 0
The problem is in your custom checker. There is no value for the variable $A, so when you multiply it by the matrix $Pstu, it acts like a blank string, and MathObjects tries to convert that to a Matrix, which produces the error you are seeing. Perhaps you meant to use \$D there instead (since the statement of the problem used $$A = D$$?