Posted by: **Alexandre Borovik** | May 11, 2011

## Online matrix calculators

This fragment from a recent email from my (first year) student is the best reason why mobile phones (which now give access to Web) should remain strictly forbidden in examinations.

>

> for Q A5 of the 2009 paper qb

>

> isnt the igen vector -1,1 ?

>

> this is what i get from, using an online calculator found here

> http://www.arndt-bruenner.de/mathe/scripts/engl_eigenwert2.htm

>

Yes, indeed, if the matrix [ 1 , 2\\ -2 , -3 ] from the exam is entered into the online calculator, it produces an eigenvector [-1\\ 1]; my answer that was questioned by my student was [1\\ -1]. Alas, computation, especially quick user-friendly automated computation, cannot replace understanding.

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