Thread Subject:

Ax=b problems...

1. polyfit(x,y,N)
About this one, I am confused about N. What decides N value?

2. what is fminsearch for? take an example...

"eric " <liangz4@uw.edu> wrote in message <k9plp5$gai$1@newscl01ah.mathworks.com>...
> 1. polyfit(x,y,N)
> About this one, I am confused about N. What decides N value?
>
> 2. what is fminsearch for? take an example...

one more question:
what is norm for? I saw err=norm(...)^2



Thank you very much

"eric " <liangz4@uw.edu> wrote in message <k9plp5$gai$1@newscl01ah.mathworks.com>...
> 1. polyfit(x,y,N)
> About this one, I am confused about N. What decides N value?
>
> 2. what is fminsearch for? take an example...

The documentation and help within matlab is pretty good. Try it!

help polyfit
doc fminsearch

~ Jos

"eric " <liangz4@uw.edu> wrote in message
news:k9plp5$gai$1@newscl01ah.mathworks.com...
> 1. polyfit(x,y,N)
> About this one, I am confused about N. What decides N value?

You decide the degree of the polynomial that you want to fit. There are
limitations, of course. You shouldn't choose N to be greater than the number
of data points minus 1 (if you do, the polynomial isn't unique) and you
shouldn't choose N to be bigger than you really need. While you _could_ fit
a 100 degree polynomial to 101 data points, keep in mind that's going to
require raising each of your x values to the 100th power and you're almost
certain to end up with an ill-conditioned system.

> 2. what is fminsearch for? take an example...

See the documentation; it contains several examples of how to use
FMINSEARCH.

http://www.mathworks.com/help/matlab/ref/fminsearch.html

If after reading that and running the examples step-by-step you still have
specific questions, feel free to post them.

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Steve Lord
slord@mathworks.com
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