title: Matlab symbolic eigenvectors
body: <p>I am trying to calculate the symbolic eigenvalues and vectors of matrices of the form</p>
  
  <pre><code>[ a, c, 0]
  [ c, b, e]
  [ 0, e, f]
  </code></pre>
  
  <p>in matlab (replace a,b,c etc with some expressions containing x, y, z). When I have 4 off diagonal terms 0 then the program is succesful. But when the matrix has only two off diagonal elements zero (like as in the example), the program fails to find eigenvectors but can find eigenvectors (which is expected since it is third degree polynomial). The expression for the eigenvalues is ofcourse quite hectic. And when I try to calculate eigenvectors it gives the error</p>
  
  <pre><code>Warning: basis of eigenspace for eigenvalue - 1/2*((c^2*d^2*e^2 -...
  Error: Unable to find eigenvectors. [mleigenvectors]
  Error in ==&gt; sym.eig at 74
  S = mupadfeval('mleigenvectors',A);
  </code></pre>
  
  <p>I am using matlab R2009a. Is this a problem that can be solved by for instance R2009b or better servers or it is just to many calculations to try? This does not seem plausible to me since if you take the above matrix subtract LI (where K is for eigenvalue I is id matrix) from it and try to solve the eigenvector equation, you can even solve it by hand to get expressions containing L, a,b,c,e,f,g. Then what you have to do is to simply put in expressions for lambda. However ofcourse the result will be very long so I am wondering if this is some memory issue?</p>
  
  <p>Thanks</p>