Find the max amplitude of Frequency from text file

Question

vu ngothanh 2015-5-13

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评论： vu ngothanh 2015-5-13

I have a text file like this

000000,-1.721511E-5,-2.869001E-5
906250E-5,-1.859251E-5,-3.247638E-5
812500E-5,-2.083079E-5,-2.504133E-5
000117,-1.996991E-5,-2.779505E-5
000156,-1.866138E-5,-3.044551E-5
000195,-2.241480E-5,-2.982592E-5
000234,-2.027983E-5,-2.579860E-5
000273,-1.786938E-5,-2.497249E-5
000312,-1.910904E-5,-2.741642E-5
.......
000352,-1.749059E-5,-2.748526E-5
000391,-2.141618E-5,-2.855233E-5
000430,-2.062418E-5,-2.751968E-5
000469,-1.817929E-5,-2.696894E-5
000508,-1.511457E-5,-3.030782E-5
000547,-1.931565E-5,-2.597071E-5
000586,-1.855808E-5,-3.158142E-5
000625,-2.072748E-5,-3.054877E-5
000664,-2.072748E-5,-3.171910E-5
000703,-1.917791E-5,-3.047993E-5
000742,-2.289689E-5,-2.486922E-5
000781,-2.165723E-5,-2.941286E-5
000820,-2.076192E-5,-3.068646E-5
000859,-1.776607E-5,-2.583303E-5
000898,-1.728398E-5,-2.748526E-5

First colum is value of time, Second and 3rd colum is value of frequency at point 1 and 2. I need to get the max and the second max value of amplitude of frequency at point 1, because maybe there are some bad value of amplitude of frequency at point 1. Then, I need to export the value of the range in the black box. How can I do it.

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Answer 1

Abhiram Bhanuprakash 2015-5-13

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Hi Vu,

In your case, since you have only text data (without character strings), I think you can save your data into a CSV file, and use 'csvread' to import the data into the MATLAB workspace. Documentation for 'csvread' is here

After you get the data into MATLAB, you can use it for further processing. For example, in your case, you can use something like:

a = csvread('data.csv'); %where data.csv file contains the data which you have pasted here
maxval = max(a(:,2)); %maximum of second column

To import data from a general text file, you can use 'textscan'. Documentation here

Hope this helps,

Cheers!

Abhiram.

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Abhiram Bhanuprakash 2015-5-13

@vu: Sorry but I am not able to understand you. As Walter has asked, can you please define what you mean by a cycle?

vu ngothanh 2015-5-13

http://en.wikipedia.org/wiki/Frequency cycles in my mean is T which T=1/f so hard to explain. sorry about that

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Answer 2

Walter Roberson 2015-5-13

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fid = fopen('YourFile.txt');
C = textscan(fid, '%f,%f,%f', 'CollectOutput', 1);
close(fid);
point1 = C{1}(:,2);
[up1, upa] = unique(point1);
maxp1 = up1(end);
maxp1pos = upa(end);
max2p1 = up1(end-1);
max2p1pos = upa(end-1);

Note that you have not clearly defined "second maximum" if what you might have is a peak over several values rather than a single bad point.

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vu ngothanh 2015-5-13

Hi Walter,

My file content the FREQUENCY of one element in a short time. In my file, to show 1 cycle, it need alot of value. I think, if we remove the biggest value to get the second biggest value like that, it can be done, but, that second value like that may be in the same cycle. I need the second max value but in the different cycle. Do you mean what I say. Sorry, my english is not too good.

Thank you for your time.

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