Is there any limitation for the number of rules and the number of membership functions that we define for a particular problem? The more the number of membership functions i define, the more accurate the modeling is, with negligible amount of error. Is that a right way or is there any restriction in the number of membership functions that i define.
Practicly, there is no limitations, generaly speaking from user of tool perspective. only significant limitation is CPU power and memory buffer of PC used for calculating. More rules, more CPU and memory needed to calculate epochs.
in MATLAB's FL toolbox
no. of memberships functions per variable is restricted to 9. and with that we can write its rules.
it is based on my experiments. may not be correct. while experimenting i was restricted to 9 mf's per variable.
Also, simulation time may increase with increased functions and rules.
Further, if looking for hardware implementation better reduce the no.of membership functions thereby reducing the complexity.
Miss Lily,
In my view, as far as the number of membership functions and the rules are concerned, system computing time should carry less importance than the complexity of framing rules .
The major aspect of large number of membership functions and consequently large number of rules (not always) is that it makes the rule formulation a bit complex task.
Though large number of MFs may provide you a highly precise non-linear empirical relation between the inputs and outputs, I still recommend not to exceed the number of MFs than 6 or 7 at the most.
Another reason is when you frame your Inference mechanism (overlapping, range of various MFs of different variables), you may or may not have enough datapoints to represent all the fuzzy numbers almost equally.
Arriving at robust FIS in this situation can serve the purpose of training the model, but it may create problem while validation of the model with the remaining datapoints (or some other dataset).
These intricacies we come across by exercising large number of trials with different combinations. These observations are difficult to understand from the texts.
With Regards
Ashu
Thanks all.
@Mr.Paul Davis: Though the drop down menu shows only a maximum of 9 MF's, its not restricted to 9. You can again select 'AddMF" and add as many MF you need.
practically, there is no limitation on the number of rules and fuzzy sets defined in the fuzzy rule base system. However, the time is key factor to constraints in required computation in fuzzy inference.
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