What a fool am i, your example is already an eigenvalue problem : you are searching the eigenvalues of [0 , 1 ; -c/a , -b/a]. So the alternative algorithm when catching a Nan could be to ask lapack to solve that for you, for example with a Schur decomposition.

Nicolas
 

ncellier at ifrance.com:
 
The example is not very good because we cannot figure why we need two algorithms here. But think of solving an eigenvalue problem or a Riccati equation, then we have several possible algorithms an could retry with matrix balancing or with another   algorithm before giving up with an error notification.

Nicolas



 
 
  

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