different general polynomial fit results

[hdruyts]

Hello,

I've encountered a strange problem using the general polynomial fit: It seems that the outcome of this vi is computer dependent...

I'm using labview 8.2.1, and tried to use the vi to get a polynomial fit (with an order between 12 and 20) on about 450 datapoints, which seemed to work fine... until I shared my vi with another person, where different results for the polynomial coefficients were obtained with the same datapoints (and the same parameter settings). I noticed that the differences get bigger when the requested order increases.

 has anybody encountered a similar problem?

greetings,

Hans

[altenbach]

Well, taking a 20th order polynomial does not make a lot of sense anyway. What are you trying to achieve? There are probably better ways to do whatever you want to do here. You are dealing with extreme intermediary values (e.g. 1500^20=3.32e+63) so a slight reordering in operation could change the outcome.

Can you explain the differences between the computers? Is the other a different OS (e.g. mac vs windows)? Just curious.

[hdruyts]

the computers I've used are all laptops running under windows xp (service pack 3)...

the main reason for using polynomials is the ease of finding roots and derivatives, but your absolutely right about the intermediary values!