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### Using fuzzy logic to solve a third degree polynomial function

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```Hello,
I would like to use fuzzy logic to solve a third degree polynomial equation. The equation looks like y=2*x^3 + 1.2*x^2 -x in the range -1.4<x<0.8
First, I would like to start by using 3 or 4 rules the I will add 2 or 3 rules to increase the accuracy.
I started to divide the main graph into 3 straight lines. The first one -1.4<x<0.7, the second one -0.7<x<0.3 and the last one 0.3<x<0.8. I tried different membership functions but it did not work.
I was wondering what the input and the output membership functions should be. I appreciate any help to solve this problem
```
 0

```"Ali Ali" <carlossentino@hotmail.com> wrote in message
news:hop32i\$i4\$1@fred.mathworks.com...
> Hello,
> I would like to use fuzzy logic to solve a third degree polynomial
> equation. The equation looks like y=2*x^3 + 1.2*x^2 -x in the
> range -1.4<x<0.8

Why are you using fuzzy logic for such a simple problem rather than
something like ROOTS?  Or is the fact that the problem is easily solvable
the point and you're trying to learn how to work with fuzzy logic?

*snip*

--
Steve Lord
slord@mathworks.com
comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ

```
 0

```"Steven Lord" <slord@mathworks.com> wrote in message <hoqbrd\$rfi\$1@fred.mathworks.com>...
>
> "Ali Ali" <carlossentino@hotmail.com> wrote in message
> news:hop32i\$i4\$1@fred.mathworks.com...
> > Hello,
> > I would like to use fuzzy logic to solve a third degree polynomial
> > equation. The equation looks like y=2*x^3 + 1.2*x^2 -x in the
> > range -1.4<x<0.8
>
> Why are you using fuzzy logic for such a simple problem rather than
> something like ROOTS?  Or is the fact that the problem is easily solvable
> the point and you're trying to learn how to work with fuzzy logic?
>
> *snip*
>
> --
> Steve Lord
> slord@mathworks.com
> comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ
>

Yes I just want to play with fuzzy logic to solve a third degree polynomial starting with 3 to 4 rules, after that I want to show that if we add more rules, the accuracy should be improved.
I appreciate your help if you can suggest just 1 rule, type of input and output memberships and I can continue.
```
 0

```"Carlos " <carlossentino@hotmail.com> wrote in message
news:hoqhum\$iv0\$1@fred.mathworks.com...
> "Steven Lord" <slord@mathworks.com> wrote in message
> <hoqbrd\$rfi\$1@fred.mathworks.com>...
>>
>> "Ali Ali" <carlossentino@hotmail.com> wrote in message
>> news:hop32i\$i4\$1@fred.mathworks.com...
>> > Hello,
>> > I would like to use fuzzy logic to solve a third degree polynomial
>> > equation. The equation looks like y=2*x^3 + 1.2*x^2 -x in the
>> > range -1.4<x<0.8
>>
>> Why are you using fuzzy logic for such a simple problem rather than
>> something like ROOTS?  Or is the fact that the problem is easily solvable
>> the point and you're trying to learn how to work with fuzzy logic?
>>
>> *snip*
>>
>> --
>> Steve Lord
>> slord@mathworks.com
>> comp.soft-sys.matlab (CSSM) FAQ:
>> http://matlabwiki.mathworks.com/MATLAB_FAQ
>
> Yes I just want to play with fuzzy logic to solve a third degree
> polynomial starting with 3 to 4 rules, after that I want to show that if
> we add more rules, the accuracy should be improved.
> I appreciate your help if you can suggest just 1 rule, type of input and
> output memberships and I can continue.

Sorry, fuzzy logic isn't my area of expertise.  Have you taken a look at the
demos that come with Fuzzy Logic Toolbox?  You can open these demos by using
the command:

demo toolbox fuzzy

You should be able to adapt part of one of these demos to do what you want.

--
Steve Lord
slord@mathworks.com
comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ

```
 0

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7/23/2012 1:46:11 AM