Strange behavior: random and plot

*To*: mathgroup at smc.vnet.net*Subject*: [mg102726] Strange behavior: random and plot*From*: Don Krug <krugd at nku.edu>*Date*: Sat, 22 Aug 2009 03:36:55 -0400 (EDT)

Hi group. I am new here and discovered some strange behavior (to me.) Hope someone can help. I will be teaching a course on programming with Mathematica this semester and so you may hear from me some more. I define ran[x_]:=Random[Real,x] If I evaluate ran[3]-ran[3] I get a non-zero result as expected. But if I do Plot[ ran[x]-ran[x] ,{x,0,3}] I get an empty axes system. I assume it is the plot of the zero function. I also know that if I set ran2[x_]:=Random[Real,x] then I get a non-zero plot as expected when I do Plot[ ran2[x]-ran[x] ,{x,0,3}] I am guessing the plot command is evaluating things in a strange way that forces the two instances of ran to be the same. Can anyone explain why? Thanks Don Krug Northern Kentucky U