Running area under the curve at each time step.

Question

Jozef 2013-2-10

0
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https://ww2.mathworks.cn/matlabcentral/answers/62915-running-area-under-the-curve-at-each-time-step

Hello,

In the problem that I am working on, I am given an x and y set of data. The x being the time and the y being ft/s^2. I need to find the running area under the curve because that will be the velocity, needless to say I am having some troubles. The code is below

My code: 
clear;
A=csvread('exc2.csv') %read data file
x=A(:,1) 
y=A(:,2)
for i=1:length(A) %run the length of the array
  v(i)=trapz(x(i),y(i)) %integral at each point 
end
plot(x,v) %plot integration over same time step

I get an error stating "ORDER contains an invalid permutation index."

Am I at all on the right track for trying to solve this?

Thank you.

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Answer 1

ChristianW 2013-2-10

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https://ww2.mathworks.cn/matlabcentral/answers/62915-running-area-under-the-curve-at-each-time-step#answer_74488

在 MATLAB Online 中打开

Your input to trapz is a single point, you want to input a line. And for n = length(x) acceleration points you can only get n-1 velocity points.

clear;
x = 0:10; 
y = sin(x);
for i=2:length(x) %run the length of the array
  v(i-1) = trapz(x(1:i),y(1:i)); % integral at each point 
end
subplot(211),plot(x,y)
subplot(212),plot(x(2:end),v)