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Re: How to find global and local maxima using octave and its position


From: preeti gaikwad
Subject: Re: How to find global and local maxima using octave and its position
Date: Mon, 17 Oct 2011 17:32:44 +0200

thanks Ben for ur reply.....well here is the figure attached....just a small description...
First peak is reference peak
second small peak is unwanted signal (top right on the big peak) which I want to remove......

so I want to get the max (amplitude) and position of first peak (which u already explained) now second peak amplitude and position and then third big bump position and amplitude.....after that I am using leasqr to fit this data....thanks for ur help.....

   

On 17 October 2011 17:21, Ben Abbott <address@hidden> wrote:

On Oct 17, 2011, at 11:04 AM, preeti gaikwad wrote:

> On 17 October 2011 15:55, Ben Abbott <address@hidden> wrote:
> On Oct 17, 2011, at 9:15 AM, preeti gaikwad wrote:
>
> > Hello all,
> >
> >                If I have x and f(x) I want to find out the maxima of f(x) and position of the same so for that if I write the syntax like "max(f(x))" I will get it but how to get its position means the corresponding x value????
> >
> > Now suppose I have 'n' value of x and f(x), and there I have three peaks in the f(x) where one peak is the "reference peak" where I want to find (its position and amplitude, width) and fit with the Gaussian function, second peak coming from the actual sample. and the third is the unwanted peak in the sample (called the noise).
> >
> >  using octave I want to get rid of this noise peak where I know want to know the width and the position to remove this
> >
> > 1. If I say max(f(x)) then I get only one peak at but how to write syntax for getting position??? I already knew the width of this pulse but how to find the width of the noise pulse????
> > 2. how to find second peak its position and width?
> > thanks a lot in advance for solving my problem........
>
> You just need the second output of the max() function.
>
>        [max_value, index_of_max_value] = max (f (x));
>
> See "help max" for more info.
>
> You can also do ...
>
>        index_of_max_value = find (f(x) == max(f(x)));
>
> Ben
>
> Thanks a lot Ben.......But I just do not understand the second output of the max() function is giving the position of the f(x) but still I have to find the max of second peak?? and that is not giving in the help max could you please help me for the same? thanks a lot in advance......

Sorry, I had skimmed your email, and tried to answer "1." I should have read your entire email more carefully.

Can you provide more information? May be a plot of the signal?

Ben



--
preeti gaikwad

Attachment: figure(1).eps
Description: PostScript document


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