I did a quick scan on a old Microrim article I just looked up..
It's not formatted, but I think you can pick out what you need..
Generating Random Numbers
The basic procedure for generating a random number is to start with a seed number and then perform calculations on the seed number to generate the actual random numbers. Often the random number generated is used as the seed number for the next iteration. The thousandths part of the time format is used as the seed number in an R:BASE command file to generate random numbers. Various SuperMath functions and other arithmetic operations generate the random number. The calculations can be simple or complex; often the simpler calculations generate the more random number.
The following examples of calculations that generate a random number use the same seed number each time and also use the complete time value in the calculation. The time format is set so that it looks like a number.
SET TIME FORMAT hhmmss.sss
SET VAR vtime DOUBLE = (.#TIME)
SET VAR vrandoml = +
(NINT(((IFRC(.#TIME))"100)/(NINT(.vtimel)/10000))) SET VAR vrandom2 = +
(IFRC(.#TIME)+NINT(LOG(.vtimel))+NINT(SORT(.vtimel)))
With the calculation based on time, you are more likely to generate duplicate numbers when the numbers are calculated in a WHILE loop one right after the other. This example uses the calculated random number as the seed number for the next iteration and generates fewer duplicate numbers. The numbers are loaded into a table.
-- set the time format so it displays like a number SET TIME FORMAT hhmmss.sss -- initialize variables
SET VAR vloop INTEGER = 0, +
vseed INTEGER= (IFRC(.#TIME)), +
vtimel DOUBLE = .#TIME, +
vmult = (NINT(.vtimel )), +
vincrement = (J DATE (.#DATE)), +
vmod = 65536 WHILE vloop < 1000 THEN
calculate the random number, this is used as
the seed number for the next iteration
SET VAR vseed = (+
(.vseed * .vmult+.vincrement)/.vmod)
if the maximum random number is reached,
reset the seed
IF vseed = 32767 THEN
SET VAR vseed = (IFRC(.#TIME))
END IF
IF ( vseed IS NULL OR vseed = 0) THEN ELSE
-- store the random number in a table and -- increment the loop counter INSERT INTO random (rand#) VALUES
SET VAR vloop = (.vloop + 1)
ENDIF ENDWH RETURN
12 July/August R:BASE Exchange
To check the randomness of your calculation, generate 1000 numbers and then graph the result.
You can see that the frequency of the numbers is random. There is no pattern even though duplicate numbers might be generated.
To generate a set of unique random numbers, check to see if the number has already been loaded to the table.
SELECT COUNT(rand#) INTO vtest + FROM random WHERE rand#=.vseed IF (vseed IS NULL OR vseed = 0) OR + vtest <> 0 THEN
ELSE
INSERT INTO random (rand# ) VALUES vseed SET VAR vloop = (.vloop + 1) ENDIF
An IF statement does not require commands in the "true" part. Sometimes, it is easier to structure the IF statement to check for a true condition, but only execute commands when the condition is not true (the ELSE part of the IF statement). The opposite condition for this IF statement is written using AND to join the conditions and is more difficult to construct and understand from a logic standpoint.
To generate a random number with a specific number of digits, verify that the number falls within a range. If the number is larger than the maximum value, the number is divided by 10; if the number is smaller than the minimum value, the number is multiplied by 9.
WHILE vrand > 999 THEN vrand = (.vrand/10) ENDWH
WHILE vrand < 100 THEN
vrand = (.vrand * 9) ENDWH
This example returns a three-digit random number. Change the comparison values in the WHILE statement to return a random number with a different number of digits. 0
Hope this helps
Jim Limburg
Bill Downall wrote:
Please help me remember if there is a way to "seed" the R:Base RANDOM() function.
Now, in a loop, it generates a series of random values that appear truly random and well distributed. However, If I run the same program later, it generates the SAME series of random values in the same order.
I remember Wayne -- years ago -- explaining that this is a behavior useful in testing, and that there was a way to make it truly random. I thought it was a separate command like RANDOMIZE, but I can't find that.
Thanks for your help.
Bill
