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Nov 4th, 2009

Generating random nos without using random module

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I have to write a code for generating random numbers without using random module and its function.
How do I do it? I tried using the system time as it keeps on changing (importing milli seconds) but with tht I am able to get random nos in the range of thousand only.

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sanchitgarg

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Nov 4th, 2009

Re: Generating random nos without using random module

Click to Expand / Collapse Quote originally posted by sanchitgarg ...

I have to write a code for generating random numbers without using random module and its function.
How do I do it? I tried using the system time as it keeps on changing (importing milli seconds) but with tht I am able to get random nos in the range of thousand only.

Well there are several algorithms to generate random number, simplest to my knowledge being Linear congruential generator(LCG).

The general formula for LCG is $X_{n+1} = \left( a X_n + c \right)~~\bmod~~m$ . The recommended value for a, m, c are given in Wikipedia page. It is recommended use those combinations of a, m, c for more randomness. Start with any value of X and for different random numbers everytime you run code choose X using system time.

To get number in particular range, eg [L, H) apply this to every random number generated(say Y) :
Z = L + Y%(H-L)

Last edited by vishesh; Nov 4th, 2009 at 12:05 pm.

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Nov 4th, 2009

Re: Generating random nos without using random module

A time based random number generator will only work if called once, or uses the random time between a user input event.

The function time.time() only updates 18.2 times per second, too slow if you request several random numbers quickly.

Last edited by vegaseat; Nov 4th, 2009 at 1:13 pm.

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Nov 4th, 2009

Re: Generating random nos without using random module

Click to Expand / Collapse Quote originally posted by vegaseat ...

A time based random number generator will only work if called once, or uses the random time between a user input event.

The function time.time() only updates 18.2 times per second, too slow if you request several random numbers quickly.

yeah i am facing many problems using time. also it generates a sequence of nos in a ascending order.

i have written a code for nos between 1 to 100. here it is:

import datetime
from time import sleep
l=[]
tym=[]

n=int(raw_input("Enter the no. of numbers to be generated"))

for i in range (n):
time=datetime.datetime.now()
t=time.microsecond

l.append(t)
sleep(0.012)

print l

for i in (l):
tym.append(i/10000)

print tym

tats why I asked for some other logic which does not have a limited range.

sanchitgarg

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Re: Generating random nos without using random module

Click to Expand / Collapse Quote originally posted by vishesh ...

Well there are several algorithms to generate random number, simplest to my knowledge being Linear congruential generator(LCG).

The general formula for LCG is $X_{n+1} = \left( a X_n + c \right)~~\bmod~~m$ . The recommended value for a, m, c are given in Wikipedia page. It is recommended use those combinations of a, m, c for more randomness. Start with any value of X and for different random numbers everytime you run code choose X using system time.

To get number in particular range, eg [L, H) apply this to every random number generated(say Y) :
Z = L + Y%(H-L)

I tried using this formula. It works fine for small nos (not exactly small but upto 1000000000) After that it starts giving L at the end of the no. How do I increase its range?

sanchitgarg

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Re: Generating random nos without using random module

You mean output sort of this 132434454545435435L.

Well this happens when the number gets greater than usual integer type range. Python converts normal integer into Long type and Python shows L after long types. When you do print num, L doesnt shows up.

Last edited by vishesh; Nov 4th, 2009 at 4:29 pm.

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Re: Generating random nos without using random module

Click to Expand / Collapse Quote originally posted by vishesh ...

You mean output sort of this 132434454545435435L.

Well this happens when the number gets greater than usual integer type range. Python converts normal integer into Long type and Python shows L after long types. When you do print num, L doesnt shows up.

print num means? Could you please tell the syntax. I want to print a list of nos.

sanchitgarg

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Re: Generating random nos without using random module

What I mean is instead of directly printing whole list, you have to print numbers individually, to avoid L at end:

Python Syntax (Toggle Plain Text)
for x in rand_num:
   print x
for x in rand_num:
   print x

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Re: Generating random nos without using random module

Is there any other method or logic except that formula?

sanchitgarg

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Re: Generating random nos without using random module

Click to Expand / Collapse Quote originally posted by vishesh ...

Well there are several algorithms to generate random number, simplest to my knowledge being Linear congruential generator(LCG).

The general formula for LCG is $X_{n+1} = \left( a X_n + c \right)~~\bmod~~m$ . The recommended value for a, m, c are given in Wikipedia page. It is recommended use those combinations of a, m, c for more randomness. Start with any value of X and for different random numbers everytime you run code choose X using system time.

To get number in particular range, eg [L, H) apply this to every random number generated(say Y) :
Z = L + Y%(H-L)

Probably the best inputs is date/time, used memory, random user input, and my favorite mouse movement(truecrypt uses this).

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