
Re: Testing a random integer generator
Posted:
Apr 8, 2013 12:05 AM


On 4/6/13 at 9:53 PM, c_mcinnis@hotmail.com (Clif McInnis) wrote:
>I am trying to test the random integer generator in a program to >make sure that it gives the type of output that I am looking for. I >expect it to generate (p<>q)<10 slightly less than 1/8 of the time >and (p=q)<10 slightly more than 1/8 of the time, 9<(p<>q)<20 >slightly less than 3/8 of the time, and 9<(p=q)<20 slightly more >than 3/8 of the time. Regardless of my expectations I would like to >see how the numbers actually come out, and to that end was >attempting to test the test the code, but I can not get it to >generate (print) any numbers. I am sure that I have made an error >somewhere in the code, but I can not find it and am not getting any >error messages. Thank you for any and all help.
>Initialization :> ({x = 0, p = 0, q = 0})
The line above is the reason the code never prints a value. It does not set x,p or q to 0. Look up RuleDelayed in the documentation center. Change this to
x=0;
and your While loop will print values
>While[x < 100, { >Clear[p, q],
the line above accomplishes nothing. It is not necessary in Mathematica to clear variables before using them.
>q = RandomInteger[{1, 4}], If[q < 4, >{p = RandomInteger[{10, 20}], >q = RandomInteger[], >If[q == 1, q = p, q = RandomInteger[{10, 20}]]}, {p = RandomInteger[{1, 9}], >q = RandomInteger[], >If[q == 1, q = p, q = RandomInteger[{1, 9}]]}], Print[p], >Print[q]}; x++]
Note a better choice when you simply want to execute a section of code n times is Do rather than While. The code below:
Do[ {q = RandomInteger[{1, 4}]; If[q < 4, p = RandomInteger[{10, 20}]; q = RandomInteger[]; If[q == 1, q = p, q = RandomInteger[{10, 20}]], {p = RandomInteger[{1, 9}], q = RandomInteger[], If[q == 1, q = p, q = RandomInteger[{1, 9}]]}], Print[p], Print[q]}, {100}]
does exactly the same as your code without the need for x.
Also, Print sends its output to $Output. So, unless you redefine $Output, you won't capture the results of your generator for further analysis.
an efficient way to capture the output would be as follows:
output = {}; Do[ {q = RandomInteger[{1, 4}]; If[q < 4, p = RandomInteger[{10, 20}]; q = RandomInteger[]; If[q == 1, q = p, q = RandomInteger[{10, 20}]], {p = RandomInteger[{1, 9}], q = RandomInteger[], If[q == 1, q = p, q = RandomInteger[{1, 9}]]}], output = {output, p, q}}, {100}]
This captures all of the p,q values in a nested list which can be made into a simple list using Flatten. That is you can do
Histogram[Flatten@output]
to create a histogram of p,q values. Or
Mean[Flatten@output] to compute the mean value and so on.

