Changing the unknown variable in a matlab line

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zozo 2012-8-16

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采纳的回答： Azzi Abdelmalek

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I have the following line in matlab:

y=sum(bin(xout>xout(1) & xout < -lim));

In the above line, Iam computing the value 'y' from known row-vectors 'bin' , 'xout', and known value 'lim'

How can I write the above equation, if I want to compute the value 'lim' if the value 'y' and row-vectors 'bin', 'xout' are now known.

%%---- Following scenario ---%% PICTURE ADDED

http://i45.tinypic.com/2a50njo.png

Please help

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zozo 2012-8-16

no..its random

Azzi Abdelmalek 2012-8-16

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do you mean bin(1x6000) and xout(1x200)? because with bin(1x200) and xout(1x6000).

y=sum(bin(xout>xout(1) & xout < -lim));

don't work

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Azzi Abdelmalek 2012-8-16

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编辑：Azzi Abdelmalek 2012-8-16

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Example: run this to find y

 bin=rand(20,1);xout=rand(20,1);lim=-0.5;
 y=sum(bin(xout>xout(1) & xout < -lim));

then run this to find lim

 lim=[];
 for k=1:length(xout);
     if sum(bin(xout>xout(1) & xout < xout(k)))==y;
         lim=[lim -xout(k)]
     end
 end
 lim=max(lim)

note: you will notice that lim is not exactly the same as the first. and if lim contains many values, you choose the bigest (-lim will be the smaller)

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Azzi Abdelmalek 2012-8-16

编辑：Azzi Abdelmalek 2012-8-16

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if y is given by

y=sum(bin(xout>xout(1) & xout < -lim));

lim can't be empty, unless you impose y. in this case, it's possible that lim will be empty

zozo 2012-8-16

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I changed:

if sum(bin(xout>xout(1) & xout < xout(k)))==y;

if sum(bin(xout>xout(1) & xout < xout(k)))<=y;

and now it works! Thanks Azzi

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Image Analyst 2012-8-16

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How about (untested)

% Get area as function of xout.
cumulativeSum = cumsum(bin);
% For a given area, called desiredArea, 
% find the index where the cumulative sum first exceeds that area.
lim = find(cumulativeSum >= desiredArea, 1, 'first');
% lim was the index.  Now find the xout value at that index:
xOutValue = xout(lim);