NIntegrate and Plot
- To: mathgroup at smc.vnet.net
- Subject: [mg63859] NIntegrate and Plot
- From: "Peter Rolnick" <abrahams_rolnick at sbcglobal.net>
- Date: Thu, 19 Jan 2006 00:03:03 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
Hello. I have a 3D function that I am integrating numerically, and it has a parameter, q. As far as I can tell, the integrand is never infinite or complex. When I use NIntegrate for a particular value of q, it does the numerical integral and gives me a reasonable value for the result (for q = 0 it gives me the expected analytic value). I can do this for many values of q, and it seems to work just fine. However... when I try to Plot the numerical integral as a function of q, though it does actually give me a reasonable plot, it also gives me this message: It gives the message repeatedly, always at the same values of k, X, and gamma (the variables of integration). There is nothing weird or singular at those points, and if I ask the numerical integral to skip any or all of those points, it gives the same message at some slightly different points. This makes me think that the problem does not have to do with those particular points. (It does this weird behavior even if I just use the Real part of the integrand, so it can't be that the value of the integrand is complex anywhere.) So my question is, why does Mathematica let me do NIntegrate for a single value of q, but get upset if I try to Plot the numerical integral over a range of values of q (even though it actually ends up doing what I asked it to do)? I'm suspecting this is some simple but subtle quality of Mathematica that has to do with using the function NIntegrate inside the function Plot. Thanks very much. Peter Rolnick Peter Rolnick, <mailto:prolnick at truman.edu> prolnick at truman.edu 216 N New St, Kirksville MO 63501, 660-665-2703 <http://www2.truman.edu/~prolnick> http://www2.truman.edu/~prolnick
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