computing area between 2 curves

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Vijay 2012-7-3

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I have two curves from the 2 vetctors as a result of simulation. I want to find the area between these 2 curves. The curves are intersecting many times.

any ideas are appreciated!!

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Answer 1

AC 2012-7-4

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Hi,

From scratch, you could try something like:

1/2*(abs(C1(2:end)-C2(2:end))+abs(C1(1:end-1)-C2(1:end-1)))*diff(I)'

where C1 and C2 are your curves and I the x-axis.

This will give you an estimate of the integral of C1(t)-C2(t) dt for t in I.

Cheers,

AC

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Luffy 2012-7-9

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 see doc diff
If X is a vector, then diff(X) returns a vector, one element shorter than X, of differences between adjacent elements.

Vijay 2012-7-23

if X is a vector from 1:10 say X-axis. then diff(X) is a vector of '1' nine times. What is the use of multiplying it??

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Answer 2

Luffy 2012-7-3

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If u know the vectors then try using polyarea & subtract them

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Luffy 2012-7-4

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 I put too much thought into it,ws thinking about finding area covered by each curve with x axis and then subtracting them to get area between them.
 Happy to know polyarea helped you

AC 2012-7-4

Hi,

Substracting the two areas is ok if the curves don't cross and you substract in the right order (that is: highest - lowest). Otherwise you will end up with a wrong result. For example, take sin(x) and cos(x) between 0 and 2: int cos(t)-sin(t) dt = -0.5 approx. int abs(cos(t)-sin(t)) dt= 1.33 approx.

It's the second one that you want. So you should compute the area of the difference in absolute value (see my response below). Cheers,

AC

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