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From: <HIDDEN>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Integration
Date: Wed, 22 Feb 2012 04:15:12 +0000 (UTC)
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"steingre" wrote in message <ji1bhj\$cvt\$1@newscl01ah.mathworks.com>...
> lambda(1)=1/8;
> Num=10000;
> for i=1:Num
>       y(i,1) = i*10/Num;
>       z(i,1) = exppdf(y(i,1),(1./lambda(1,1)));
> end
> trapz(y,z)
>
> Why do I not get 1?
- - - - - - - - -
You haven't gone far enough out in the range of y to approximate infinity.  You have stopped where y is equal to 10 which makes exppdf equal to 1/8*exp(-10/8) = .0358 .  This is not nearly far enough.  Also you started at y = 0.001 instead of zero, another source of error.  Finally, you should not expect exact answers because trapezoidal integration is only a numerical approximation to the ideal integral value.

By the way, you *are* using uniform spacing here.  Each interval in y is 0.001 .

Roger Stafford
```