how do i generate random numbers in an interval?

ieatsoupwithafork

Hi,

Title says all. I know the ? operator but I have no idea how to put it to practical use. Spin doesn't have a random function like I'm used to with other languages so I have no idea how and what to do with "?". Any help would be greatly appreciated.

Cheers!

Publison

There is a Random Number Generator in the OBEX:

http://obex.parallax.com/object/498

Publison

Type "Random" in the upper right search box and it will bring up some threads about Random generation.

Phil Pilgrim (PhiPi)

Try this in your program:

VAR
  long seed

PUB random(lo, hi)
  return lo + ?seed // (hi - lo)

It will return a random number between lo and hi - 1.

-Phil

Electrodude

Phil Pilgrim (PhiPi) wrote: »

Try this in your program:

VAR
  long seed

PUB random(lo, hi)
  return lo + ?seed // (hi - lo)

It will return a random number between lo and hi - 1.

-Phil

Are you sure that's correct? Don't you need to strip the sign bit before the // in case the result of ?seed is negative? Otherwise, it will return numbers in the range (lo-(hi-lo+1), hi).

JonnyMac

Don't you need to strip the sign bit ...

I do that in the prng object that I liberated from @Heater.

pub randomize(lo, hi) 

'' Return a random number between lo and hi (inclusive)

  return  (random >> 1) // ((hi - lo) + 1) + lo

I also try to stick a call to the random() method in a loop so that the prng sequence is constantly being tumbled. The P2 does this for us, providing a new random # on every clock.

Phil Pilgrim (PhiPi)

Electrodude wrote:

Are you sure that's correct? Don't you need to strip the sign bit before the // in case the result of ?seed is negative? Otherwise, it will return numbers in the range (lo-(hi-lo+1), hi).

You're correct, of course. Jon has it right.

-Phil

bluejay

is there a way to randomize numbers from 1 to 70?
Thanks

JonnyMac

@bluejay said:
is there a way to randomize numbers from 1 to 70?
Thanks

In the post above there is discussion about the randomize() method from the attached object. It would go like this:

rval := prng.randomize(1, 70)

Easy peasy.

tritonium

Hi

@bluejay said:
is there a way to randomize numbers from 1 to 70?
Thanks

I wonder if you are asking for all the numbers 1 to 70 to be in a randomised order since getting a random number between 1 and 70 has already been explained.
If that is the case then build an array with the numbers 1 to 70 in it and starting at array item 1, exchange it with another number in the array, range 1-70 generated using the randomise function, and work your way through the whole array.

Dave