From: Armin Roehrl <armin@...>
Date: 2002-03-12T05:54:21+09:00
Subject: Re: painfully newbie question

Hi Damien,

	I have not tried your code, but
I think your problem is that you have 5 times
the same individual in the Array.

You can verify this by:
put
   @alive=rand 
instead of alive
Now look at your entries in the 1st round:
Alive should always be the same.

to fix this, create 5 instances of Individual
e.g.
population=Array.new
for i in 0...5
  population[i]=Individual.new(1,0)
end
puts "Bef....

hope this is what you wanted,
	A
On Monday 11 March 2002 21:25, you wrote:
> Last week I posted a question about using Ruby in
> population ecology simulation, and I am very grateful
> for the replies I got.  It seems Ruby is exactly what
> I am looking for.
>
> Of course, I have my first question/conundrum, and I
> hope it isn't too painful for experienced Ruby/OO
> programmers.
>
> I am trying to simulate "death" in an array of objects
> ("Individuals") by tossing a "coin".  However, for
> some reason, I get results I am not expecting.  Here
> is my code:
>
> #Start
>
> class Individual
>   attr_writer :alive, :mother
> def initialize(alive = 1,mother = 0)
>   @alive = alive
>   @mother = mother
> end
>
> def to_s
> "Alive: #{@alive} Pregnant: #{@mother} \n"
> end
>
> def survival
>   if rand<0.5
>     @alive = 0
>   else
>     @alive = 1
>   end
> end
>
> end
>
>
> population = Array.new(5,Individual.new(1,0))
> puts "Before random death trials: \n"
> puts population.to_s
>
> puts "During random death trials: \n"
>
> for i in 0..(population.length-1)
>   population[i].survival
>  puts population[i].to_s
> end
>
> puts "After random death trials: \n"
>
> puts population.to_s
>
> # End
>
> The output I get is:
>
> Before random death trials:
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> During random death trials:
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> Alive: 0 Pregnant: 0
> Alive: 0 Pregnant: 0
> After random death trials:
> Alive: 0 Pregnant: 0
> Alive: 0 Pregnant: 0
> Alive: 0 Pregnant: 0
> Alive: 0 Pregnant: 0
> Alive: 0 Pregnant: 0
>
> When I would expect to get:
>
> Before random death trials:
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> During random death trials:
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> Alive: 0 Pregnant: 0
> Alive: 0 Pregnant: 0
> After random death trials:
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> Alive: 1 Pregnant: 0
> Alive: 0 Pregnant: 0
> Alive: 0 Pregnant: 0
>
> The value in "Alive" seem to be copied from the last
> iteration into the array population once the for loop
> is complete.
>
> I hope this question isn't too inane for the list, but
> I am stumped and would appreciate any insight.
>
> Thank you in advance,
>
> Damien
>
>
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-- 
Armin.

-----------------------------------------------
Armin Roehrl, http://www.approximity.com
Training, Development and Mentoring
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