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Generating random number within a specific range (0.5-1.5) Generating random number within a specific range (0.5-1.5)
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Old 04-03-2009
TehOne TehOne is offline
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Generating random number within a specific range (0.5-1.5)
Hello, need a way to generate numbers within 0.5-1.5 range

Has to be totally random:

0.6
1.1
0.8
1.5
0.6
and so on....


How to?
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Old 04-03-2009
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pludi pludi is offline Forum Staff  
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Take ${RANDOM}, mod by 11, add 5, divide by 10. If that's not random enough, implement yourself a Blum-Blum-Shub-PRNG
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Old 04-03-2009
TehOne TehOne is offline
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Quote:
Originally Posted by pludi View Post
Take ${RANDOM}, mod by 11, add 5, divide by 10. If that's not random enough, implement yourself a Blum-Blum-Shub-PRNG
and how will that stay within 0.5 and 1.5 ?
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Old 04-03-2009
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The RANDOM variable will generate a random integer every time it's read, say 7081 or 17285. The modulo operation will return the remainder of a division, which can only be between 0 and divisor-1, so with 11 it's between 0 and 10. Add 5 so it's between 5 and 15. Divide by 10, and it's between .5 and 1.5

7081 % 11 = 8
8 + 5 = 13
13 / 10 = 1.3

17285 % 11 = 4
4 + 5 = 9
9 / 10 = 0.9
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Old 04-03-2009
TehOne TehOne is offline
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echo $((((RANDOM%11)+5)/10))
1
echo $((((RANDOM%11)+5)/10))
0

That's not what I need.... look my first post I gave some output examples
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Old 04-03-2009
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vgersh99 vgersh99 is offline Forum Staff  
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Quote:
Originally Posted by TehOne View Post
echo $((((RANDOM%11)+5)/10))
1
echo $((((RANDOM%11)+5)/10))
0

That's not what I need.... look my first post I gave some output examples
All ksh arithmetic is integer.
Use 'bc' for the floating point arithmetic.
something along the lines:

Code:
echo "scale=2;(((${RANDOM} % 11)+5)/10)" |bc

OR

Code:
nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'

Last edited by vgersh99; 04-03-2009 at 01:42 PM..
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Old 04-03-2009
TehOne TehOne is offline
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Quote:
Originally Posted by vgersh99 View Post
All ksh arithmetic is integer.
Use 'bc' for the floating point arithmetic.
something along the lines:

Code:
echo "scale=2;(((${RANDOM} % 11)+5)/10)" |bc

OR

Code:
nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'

Code:
[19:02:20] root:~# echo "scale=2;(((${RANDOM} % 11)+5)/10)" | bc
.50
[19:02:20] root:~# echo "scale=2;(((${RANDOM} % 11)+5)/10)" | bc
.51
[19:02:21] root:~# echo "scale=2;(((${RANDOM} % 11)+5)/10)" | bc
.50
[19:02:21] root:~# echo "scale=2;(((${RANDOM} % 11)+5)/10)" | bc
.50
[19:02:21] root:~# echo "scale=2;(((${RANDOM} % 11)+5)/10)" | bc
.50

It only gives .50 or .51 as output...

and when using quickly


Code:
nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'

it gives a couple times the same result... example:


Code:
[19:03:17] root:~# nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'
0.60
[19:03:18] root:~# nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'
0.60
[19:03:18] root:~# nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'
0.60
[19:03:18] root:~# nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'
0.60
[19:03:18] root:~# nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'
0.60
[19:03:18] root:~# nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'
0.60
[19:03:18] root:~# nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'
1.00
[19:03:19] root:~# nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'
1.00
[19:03:19] root:~# nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'
1.00
[19:03:19] root:~# nawk 'BEGIN {max=10000;srand(); printf("%.2f\n", ((int(max*rand())%11)+5)/10)}'
1.00

My script will be using the random command sometimes a few times within one second and having the same result each time is not an option..
Last edited by TehOne; 04-03-2009 at 02:12 PM..
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