Re: What is the problem? There are no images and no wrong reports for this small program.

*To*: mathgroup at smc.vnet.net*Subject*: [mg112310] Re: What is the problem? There are no images and no wrong reports for this small program.*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Thu, 9 Sep 2010 04:21:09 -0400 (EDT)

On 9/7/10 at 2:02 AM, justwanglunwei at gmail.com (peter) wrote: >Hello Mathematica community, I really need some help.... I realized >there are some mistakes in this program, but I can't find out what >it is, I keep trying for weeks, still there are some problem, I >never used Mathematica before >a==Exp[(-2r^2)/3]; b==BesselJ[0,(r*Sqrt[x^2+y^2])/0.8]; c==r^2= ; >d==5a; >Plot[Abs[Integrate[r*b*a*Exp[-I(c+d)]dr,{r,0,=E2=88=9E}]]^2,{x,-0.01 >,0.01}, {y,-0.01,0.01}] >=EF=BC=88I is Complex i=EF=BC=89 Your email is coming through somewhat garbled. The best way to post code in email is to select the cell in Mathematica you want to post and ensure the format of that cell is in InputForm before doing the copy/paste into email. You can make any cell be in InputForm by selecting the cell then going to the Cell menu selecting ConvertTo->InputForm. On a Mac, this also has a shortcut key of cmd-shift-I. There should be a similar shortcut on other platforms. Also, it is a good idea to avoid using special characters such as Greek symbols for something to be posted. Doing the above will make your post easier to read and avoid the problem being seen in your post. I am going to have to guess a bit as to the source of your problem. Judging by what appears to be part of an error message it looks like you might be using a complex variable for the upper integration limit. But since this part is garbled, I cannot be sure about this or if this is part of the issue. It also appears you are explicitly using dr to be have the usual meaning this has in a text. That portion of the integral should not be used when doing integration with Mathematica. The dr term will be seen by Mathematica as a separate variable with no dependence on r multiplying the other terms in the integrand. The Integrate command should be outside the Plot command or you should use Evaluate to force evaluation of the integral before Plot tries to actually plot the integral. That is g[x_] = Integrate[y Exp[y], {y, 0, x}]; Plot[g[x], {x, 0, 2}] will generate a plot reasonably quickly But Plot[Integrate[y Exp[y], {y, 0, x}],{x, 0, 2}] will also create the same plot but will run much slower since the integral is being evaluated repeatedly for every value of x Plot uses to create the graphic. Note, hear I used Set (=) not SetDelayed (:=) when defining g. Had I used SetDelayed here, there would have been no improvement in time required to generate the plot. Also, for this example, I used an integral that has a closed form solution. For integrals where no closed form solution exists there won't be much to gain by having the integral outside the Plot command. But in these cases it is probably better to use NIntegrate rather than Integrate.