MathGroup Archive 2012

[Date Index] [Thread Index] [Author Index]

Search the Archive

Bug in NIntegrate[]?

I define the function f[x] as follows:

f[x_] := 0 /; x < 0 || x > 1;
f[x_] := 1

It is zero outside of the interval [0,1]. This can be verified by plotting
Plot[f[x], {x, -1, 2}]

Now I integrate it from -1 to 2:
In[270]:= NIntegrate[f[x], {x, -1, 2}]
Out[270]= 3.

The result should be 1, but it is 3. Clearly Mathematica ignores the fact that f[x] is zero outside of [0,1].

This caused a lot of headache for me recently when I encountered such behavior in one of my research code.

  • Prev by Date: Re: Can't work with Mathematica 8
  • Next by Date: Re: fyi, small note on using Mathematica for object based programming
  • Previous by thread: Re: Can't work with Mathematica 8
  • Next by thread: Re: Bug in NIntegrate[]?