Difference between revisions of "FAQ"
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The PolynomialModel tries to do a least squares fit, based on which monomials are allowed in numerator and denominator. We have experienced that some models just find a flat model as the best least squares fit. There are two causes for this: | The PolynomialModel tries to do a least squares fit, based on which monomials are allowed in numerator and denominator. We have experienced that some models just find a flat model as the best least squares fit. There are two causes for this: | ||
| − | # The number of sample points is few, and the model parameters (as explained [[Model types explained#PolynomialModel|here]] and [[Adaptive Model Builders|here]]) force the model to use only a very small set of degrees of freedom. The solution in this case is to increase the minimum percentage bound in the xxxPolynomialInterface section of your configuration file: change the percentageBounds option to "60,100", "80,100", or even "100,100". "100,100" will force the polynomial models to always exactly interpolate. However, | + | # The number of sample points is few, and the model parameters (as explained [[Model types explained#PolynomialModel|here]] and [[Adaptive Model Builders|here]]) force the model to use only a very small set of degrees of freedom. The solution in this case is to increase the minimum percentage bound in the xxxPolynomialInterface section of your configuration file: change the percentageBounds option to "60,100", "80,100", or even "100,100". A setting of "100,100" will force the polynomial models to always exactly interpolate. However, note that this does not scale very well with the number of samples. |
# Another possibility is that given a set of monomial degrees, the flat function is just the best possible least squares fit. In that case you simply need to wait for more samples. | # Another possibility is that given a set of monomial degrees, the flat function is just the best possible least squares fit. In that case you simply need to wait for more samples. | ||
Revision as of 16:24, 16 May 2007
Installation And Configuration
Upgrading
How do I upgrade to a newer version?
Delete your old toolbox directory and replace it by the new one.
Using
I want to model my own problem
See the Adding an example page.
I want to contribute some data/patch/documentation/...
See the Contributing page.
How do I interface with the toolbox?
See the Data format page.
Troubleshooting
I have a problem and I want to report it
See the Reporting problems page.
I sometimes get flat models when using rational functions
The PolynomialModel tries to do a least squares fit, based on which monomials are allowed in numerator and denominator. We have experienced that some models just find a flat model as the best least squares fit. There are two causes for this:
- The number of sample points is few, and the model parameters (as explained here and here) force the model to use only a very small set of degrees of freedom. The solution in this case is to increase the minimum percentage bound in the xxxPolynomialInterface section of your configuration file: change the percentageBounds option to "60,100", "80,100", or even "100,100". A setting of "100,100" will force the polynomial models to always exactly interpolate. However, note that this does not scale very well with the number of samples.
- Another possibility is that given a set of monomial degrees, the flat function is just the best possible least squares fit. In that case you simply need to wait for more samples.
There is no noise in my data yet the rational functions don't interpolate
See the previous question.
When using rational functions I sometimes get 'spikes' (poles) in my model
When the denominator polynomial of a rational model has zeros inside the domain, the model will tend to infinity near these points. In most cases these models will only be recognized as being `the best' for a short period of time. As more samples get selected these models get replaced by better ones.
The RationalPoleSampleSelector was designed to get rid of this problem more quickly, but it only selects one sample at the time and therefore probably needs updating.
