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Integration via cumsum - Newsreader - MATLAB Central
http://www.mathworks.com/matlabcentral/newsreader/view_thread/27105[22/08/2013 09:36:24]
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Thread Subject:Integration via cumsum
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Subject: Integration via cumsumFrom: J A LlewellynDate: 30 Aug, 2001 16:20:35Message: 1 of 3
I have multiple sets of about 32000 points each in anacceleration data set (with close time spacing), so Iproposed, for each one, to calculate the integral toget velocity and do a second integration to getdisplacement. I looked up some old code from an earlierproject, and it looks like this ydot=cumsum(y)*delt;ydot=ydot-mean(ydot);ydis=cumsum(ydot)*delt;ydis=ydis-mean(ydis);I know it's a crude integration but what I can'tremember for the life of me is why did I do the meancorrection?While I'm at it, if there's a fast trap. or otherimprovement I'd like to know about it. It must be fast.
Subject: Integration via cumsumFrom: Boyko StoimenovDate: 31 Aug, 2001 20:54:58Message: 2 of 3
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MATLAB Central > MATLAB Newsreader > Integration via cumsum
Integration via cumsum - Newsreader - MATLAB Central
http://www.mathworks.com/matlabcentral/newsreader/view_thread/27105[22/08/2013 09:36:24]
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Hi J A Llewellyn,
> I know it's a crude integration but what I can't> remember for the life of me is why did I do the mean> correction?It's a good idea to comment your own code isn't it?You did the mean correction, becauseVelocity = Integral (acceleration) + Constant
The Constant is your initial velocity V0. You don't know it, but what youknow is that your velocity fluctuates around the zero, otherwise yourstructure will not be vibrating, it will be moving. That's why removing themean has the effect of adjusting for your unknown initial conditions.If the data is to be used for frequency analysis, consider better to useSimpson's rule. It has a better frequency response (flat up to 0.2*Samplingfrequency).Simpson's rule integration is performed with this:
b = [1 4 1]/3;a = [1 0 -1];z = filter(b,a,y)*delta;
Hope this hepls.Boyko
--On the USENET they seldom misquote you. In fact, they usually repeat word for word what you shouldn't have said.--------------------------------------------------------------------------------------------------------
Subject: Integration via cumsumFrom: J A LlewellynDate: 31 Aug, 2001 11:22:52Message: 3 of 3
Thanks Boyko, I couldn't tolerate simpson's before butI'll try it again.Tony
Integration via cumsum - Newsreader - MATLAB Central
http://www.mathworks.com/matlabcentral/newsreader/view_thread/27105[22/08/2013 09:36:24]
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