1. An Applied Algorithmic Activity:
Lets say we want to step through the numbers 1 to N, in a particular
order. The order of the numbers can be arbitrary, but each number can
only be visited once, and the order of the visits should be seeded by
a number passed to it.
For example:
1923840657
0123456798
7648235910
It seems like it needs some sort of hash value, but I couldn't for the
life of me figure out how.
How would you suggest I do this? Each seed doesn't have to generate a
unique result, but it would be nice. 
--
MrTrick
2. Re: An Applied Algorithmic Activity:
Patrick Barnes wrote:
>
> Lets say we want to step through the numbers 1 to N, in a particular
> order. The order of the numbers can be arbitrary, but each number can
> only be visited once, and the order of the visits should be seeded by
> a number passed to it.
>
> For example:
> 1923840657
> 0123456798
> 7648235910
>
> It seems like it needs some sort of hash value, but I couldn't for the
> life of me figure out how.
> How would you suggest I do this? Each seed doesn't have to generate a
> unique result, but it would be nice.
One way to do this is to iterate using a number that is relatively prime
to N. If two numbers are relatively prime, it means that their greatest
common divisor is 1.
So suppose N = 10. You could use 7, to pick a number at random, and
you would get (modulo 10, of course):
7, 4, 1, 8, 5, 2, 9, 6, 3, 0
In euphoria:
integer N, n, p
N = 10
p = 7
n = 0
for i = 1 to N do
n = remainder( n + p, N )
? n
end for
Matt Lewis
3. Re: An Applied Algorithmic Activity:
> One way to do this is to iterate using a number that is relatively prime
> to N. If two numbers are relatively prime, it means that their greatest
> common divisor is 1.
>
> So suppose N = 10. You could use 7, to pick a number at random, and
> you would get (modulo 10, of course):
>
> 7, 4, 1, 8, 5, 2, 9, 6, 3, 0
That looks good!
Now I just need a lowest common denominator function:
function lcd(atom a, atom b)
atom c
while b do
c = remainder(a, b)
a = b
b = c
end while
return a
end function
(Hooray for Eulers method - http://www.mathwizz.com/fractions/help/help3.htm )
and that'll give me a list of possible seed values.
Thanks all... this should work.
--
MrTrick
4. Re: An Applied Algorithmic Activity:
Hi Patrick,
Patrick Barnes wrote:
>
> Lets say we want to step through the numbers 1 to N, in a particular
> order. The order of the numbers can be arbitrary, but each number can
> only be visited once, and the order of the visits should be seeded by
> a number passed to it.
>
> For example:
> 1923840657
> 0123456798
> 7648235910
>
> It seems like it needs some sort of hash value, but I couldn't for the
> life of me figure out how.
> How would you suggest I do this? Each seed doesn't have to generate a
> unique result, but it would be nice.
> --
is this a function - which is from Jiri Babor - which might be helpful
for you?:
function shuffle(sequence s)
object temp
integer j
for i = length(s) to 2 by -1 do
j = rand(i)
temp = s[j]
s[j] = s[i]
s[i] = temp
end for
return s
end function
Have a nice day, Rolf
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5. Re: An Applied Algorithmic Activity:
> is this a function - which is from Jiri Babor - which might be helpful
> for you?:
>
> function shuffle(sequence s)
> object temp
> integer j
>
> for i = length(s) to 2 by -1 do
> j = rand(i)
> temp = s[j]
> s[j] = s[i]
> s[i] = temp
> end for
> return s
> end function
Unfortunately no, because of the randomness in it. The thing needs to
be reproducible again.
--
MrTrick
6. Re: An Applied Algorithmic Activity:
----- Original Message -----
From: "Patrick Barnes"
Sent: Wednesday, June 30, 2004 4:48 AM
Subject: Re: An Applied Algorithmic Activity:
> > is this a function - which is from Jiri Babor - which might be helpful
> > for you?:
...
> Unfortunately no, because of the randomness in it. The thing needs to
> be reproducible again.
>
> --
> MrTrick
include machine.e
set_rand(i1)
Set the random number generator to a certain state, i1, so that you will get
a known series of random numbers on subsequent calls to rand().
function shuffle(sequence s, integer seed)
object temp
integer j
set_rand(seed)
for i = length(s) to 2 by -1 do
j = rand(i)
temp = s[j]
s[j] = s[i]
s[i] = temp
end for
return s
end function
unkmar
