MATH
21 B
Mathematics Math21b Spring 2015
Linear Algebra and Differential Equations
Exhibit: Bad Calculator ?
Course Head: Oliver Knill
Office: SciCtr 432

A bad calculator ?

During office hours, a student once tried an online calculator to check on the eigenvectors of the matrix
 3   -1   -1   -1 
-1    2   -1    0
-1   -1    3   -1
-1    0   -1    2
Here it the command Link The result
does not agree with the output
{{4, 4, 2, 0}, {{-2, 1, 0, 1}, {-1, 0, 1, 0}, {0, -1, 0, 1}, {1, 1, 1, 1}}}
of the Mathematica command
Eigensystem[{{3,-1,-1,-1},{-1,2,-1,0},{-1,-1,3,-1},{-1,0,-1,2}}]
Still, both outputs are right? How come?

Related, an other student sent the following screenshot of a calculation. We had learned that B=A10 has the same eigenvectors than A. How come the results change? Again, its up to you to find the problem:
Please send questions and comments to knill@math.harvard.edu
Math21b Harvard College/GSAS: 1771, Exam group 3| Oliver Knill | Spring 2015 | Department of Mathematics | Faculty of Art and Sciences | Harvard University, [Canvas], [ISites]. Bookmark http://sites.fas.harvard.edu/~math21b/| Twitter