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### solve non linear equations with constraint

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```Hi,

I want to solve a set of non linear equations f[X]= Y
where
Y is a given vector has n dimensions;
X is the vector to be solved, which also has n dimensions;
I would like to add one more constraint on X such that x1+x2+...+Xn=1

I am not sure if fsolve can handle constraint or is there another function that I can utilise? Please advise on this and many thanks in advance.

J
```
 0

```"Jie " <jz286@cam.ac.uk> wrote in message <ibuve1\$7r\$1@fred.mathworks.com>...
> Hi,
>
> I want to solve a set of non linear equations f[X]= Y
> where
> Y is a given vector has n dimensions;
> X is the vector to be solved, which also has n dimensions;
> I would like to add one more constraint on X such that x1+x2+...+Xn=1
>
> I am not sure if fsolve can handle constraint or is there another function that I can utilise? Please advise on this and many thanks in advance.
=======

Why do you distinguish between this "constraint" and the other non-linear equations. Why not add this equation to your system

x1+x2+...+Xn=1

making it equation number n+1?
```
 0

```"Jie " <jz286@cam.ac.uk> wrote in message <ibuve1\$7r\$1@fred.mathworks.com>...
>
> I am not sure if fsolve can handle constraint or is there another function that I can utilise? Please advise on this and many thanks in advance.

You could also use the constraint equation to eliminate one of the variables, say x(n)

x(n)=1-(x(1)+x(2)+...+x(n-1))

You can then reformulate f[X]=Y in terms of the first n-1 variables x(i) only.

Failing that, there's always fmincon.
```
 0

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7/21/2012 12:45:49 AM