In the version of Library/TCNJ/TCNJ_Eigenvalues/problem10.pg that we have at U. C. Davis there appears to be a problem if the student's seed is 3077. In this case the eigenvalues are -8 and -6 and the eigenvectors are (1,1) and (1,0) respectively. When I, the instructor, enter these values and click on "Show correct answers" WeBWorK displays the answers thus: 1; 1; 1; 0; but says that only one of the answers is correct. A simple check (or Wolfram Alpha) will show that (1,1) and (1,0) are indeed the correct answers, but WeBWorK will not accept (1,0) as a correct answer. However, when I change the seed to 77 the problem numbers change and WeBWorK will accept the correct answers as correct.
By the way in MATLAB notation the matrix is A = [-6, -2; 0, -8].
I am not sufficiently familiar with the ins and outs of "answer rules" to have been able to debug the problem in a half hour or so. I'm attaching the problem file to this post.
- Gerry Puckett