Truncating Y values during integration to integrate only the "peaks" or delete CERTAIN elements from a matrix

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mark 2013-11-18

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https://ww2.mathworks.cn/matlabcentral/answers/106588-truncating-y-values-during-integration-to-integrate-only-the-peaks-or-delete-certain-elements-from

编辑： Azzi Abdelmalek 2013-11-18

I have a load of data from a force transducer output. The data is in the form of time vs volts.

      TEXT=fopen('Test 5.txt','rt');
      texta=textscan(TEXT,'%f%f','CommentStyle','"');
      A=texta{1};
      B=texta{2};
      C=[A,B];
      D=C;
      plot(D)

The first part of my script removes the -ve values, as this relates to the compression wave recoiling in the force transducer and doesn't actually relate to compressive forces at all.

          C(C<0)=0;
          plot(C)

So far so good.

I am measuring the peak impulse above a certain range — impulse being the integral of force*time (or volts*time in this instance as the transducer outputs a voltage and I haven't included the conversion yet).

To measure the peak impulse I only need the values above a certain range, say 1.

I have tried to simply make a conditional statement to remove all data less than 1:

          E=C;
          E(E<1)=0;
          plot(E)

However, this is not correct as what I am after is more like this (edited on MS paint):

Does anyone have any ideas on how I can, either:

Limit the Y values used to numerically integrate the data i.e ymin=1
Remove the data in such a fashion as to resemble the final image above?

Any help would be appreciated!!! Mark.

EDIT:

Please note that I cannot simply state that E(E<1)=1 as this would artificially inflate the integral. I need all the data below that point to basically disappear.

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Answer 1

Azzi Abdelmalek 2013-11-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/106588-truncating-y-values-during-integration-to-integrate-only-the-peaks-or-delete-certain-elements-from#answer_115595

在 MATLAB Online 中打开

findpeaks(y,'minpeakheight',1)

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mark 2013-11-18

Hey Azzi,

It is able to take out values of y above 1 but it fails to take the X values too.

Say a force parabola (peak) is bounded within 0.1s, it will only plot the parabola force (i.e the line) vs a row value. If there are 100 points defining the curve it'll plot the Y values vs X values going from 0->100. It should take the corresponding time interval that the peak lies within.

As you can see in the above output, there are over 800 points that define data points above 1 but it hasn't indicated the total time over which this should occur.

How do you get matlab to output the corresponding X values?
Is there really no way to just tell matlab to integrate the area under the curve starting from this value?

cheers, Mark.

Azzi Abdelmalek 2013-11-18

编辑：Azzi Abdelmalek 2013-11-18

在 MATLAB Online 中打开

[x_peak,x_location]=findpeaks(y,'minpeakheight',1)

to integrate the area under the curve, use trapz function

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Truncating Y values during integration to integrate only the "peaks" or delete CERTAIN elements from a matrix

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Truncating Y values during integration to integrate only the "peaks" or delete CERTAIN elements from a matrix

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