MATLAB: Integrating non-syms var

arrayintegratenon-symsvar

I have:

x=0:1/8000:0.03;
y=sin(x);

How do I integrate y? Essentially I need an array of values which are the values of -cos(x). I can't use symsvar because I am trying to graph y on the same plot which currently graphs an array.

Thanks in advance

Best Answer

trapz(x, y)

"I can't use symsvar because I am trying to graph y on the same plot which currently graphs an array."

That does not actually matter; you can use "hold on" before using fplot() or ezplot() .

Besides, the integral of y is going to be a single value, which you are probably not going to plot.

Perhaps you were thinking of cumulative integral, which can be plotted. For that use cumtrapz(x,y)

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MATLAB: Integrating array of functions

In this calculation i have assumed that you are doing double integration first w.r.t y then x. First define symbolic matrix. Then perform double integration.

>> syms x y
>> a=[x.^2+y x+y];
>> int(int(a,y, 0, sin(x)), 0, pi)

In this calculation y limit is from 0 to sin(x) and x limit is from 0 to pi.

MATLAB: Double & Triple Integration with tabular data

You can use Matlab's 'trapz' successively for this purpose. The easiest case is integrating over a rectangular region in (x,y) - that is, where the tabular data, T(x,y), is defined over a rectangular mesh of (x,y) values. Let x and y be vectors of the (x,y) values along the two edges of the rectangular table.

   [X,Y] = meshgrid(x,y);
   T = (The array of tabular values corresponding to X and Y)
   I = trapz(y,trapz(x,T,2));  % <-- The double integral

You should realize that the accuracy of this method is limited by how closely-spaced the x and y values are in the rectangle. For higher order integration than the trapezoidal method there are some algorithms given in the MatLab File Exchange.

Best Answer

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