brl_random.md 5.6 KB
id: brl.random title: BRL.Random
sidebar_label: BRL.Random
Random numbers
The random module contains commands for generating random numbers.
The numbers generated are not really random, as without special hardware support a software algorithm cannot produce 'real' random numbers.
Instead, the algorithm produces values that merely appear to be random. In reality, each generated value actually depends on the previously generated value.
You can set the 'state' of the random number generator using the SeedRnd command. A common practice is to seed the random number generator with the system time when your program starts up, for example:
SeedRnd MilliSecs()
````
This ensures that the random number generator does not start in the same state each time your program is run, which would cause it to produce the same sequence of random numbers.
## Types
| Type | Description |
|---|---|
| [TRandom](../../brl/brl.random/trandom) | Random number generator |
## Functions
### `Function RndFloat:Float()`
Generate random float
#### Returns
A random float in the range 0 (inclusive) to 1 (exclusive)
#### Example
blitzmax ' RndFloat.bmx ' Two players take turns shooting at a target. The first hit wins. ' Player 1 hits 30% of the time, player 2 hits 40%. ' What is the probability that player 1 wins?
SuperStrict
Function winner:Int() ' play game once, return winner 1 or 2
Repeat
If RndFloat() < 0.3 Then Return 1
If RndFloat() < 0.4 Then Return 2
Forever
End Function
Local count:Int[3]
Local trials:Int = 1000000
For Local n:Int = 1 To trials
count[ winner() ] :+ 1
Next
Print "Estimated probability = " + ( Float( count[1] ) / Float( trials ) ) Print Print " Exact probability = " + ( 15.0 / 29.0 )
<br/>
### `Function RndDouble:Double()`
Generate random double
#### Returns
A random double in the range 0 (inclusive) to 1 (exclusive)
#### Example
blitzmax ' RndDouble.bmx ' Two players take turns shooting at a target. The first hit wins. ' Player 1 hits 30% of the time, player 2 hits 40%. ' What is the probability that player 1 wins?
SuperStrict
Function winner:Int() ' play game once, return winner 1 or 2
Repeat
If RndDouble() < 0.3 Then Return 1
If RndDouble() < 0.4 Then Return 2
Forever
End Function
Local count:Int[3]
Local trials:Int = 1000000
For Local n:Int = 1 To trials
count[ winner() ] :+ 1
Next
Print "Estimated probability = " + ( Double( count[1] ) / Double( trials ) ) Print Print " Exact probability = " + ( 15.0 / 29.0 )
<br/>
### `Function Rnd:Double(minValue:Double = 1, maxValue:Double = 0)`
Generate random double
The optional parameters allow you to use Rnd in 3 ways:
<table><tr><td> <b>Format</b></td><td><b>Result</b></td></tr><tr><td> &Rnd()</td><td>Random double in the range 0 (inclusive) to 1 (exclusive)</td></tr><tr><td> &Rnd(_x_)</td><td>Random double in the range 0 (inclusive) to n (exclusive)</td></tr><tr><td> &Rnd(_x,y_)</td><td>Random double in the range x (inclusive) to y (exclusive)</table>
#### Returns
A random double in the range min (inclusive) to max (exclusive)
#### Example
blitzmax ' Rnd.bmx ' Use Rnd() to estimate area inside the unit circle x^2 + y^2 = 1.
SuperStrict
Local totalpoints:Int = 1000000 Local inpoints:Int
For Local n:Int = 1 To totalpoints
Local x:Double = Rnd( -1.0, 1.0 ) ' Generate random point in 2 by 2 square.
Local y:Double = Rnd( -1.0, 1.0 )
If x*x + y*y < 1.0 Then inpoints :+ 1 ' point is inside the circle
Next
' Note: Ratio of areas circle/square is exactly Pi/4.
Print "Estimated area = " + ( 4.0 * Double(inpoints)/Double(totalpoints) ) Print Print " Exact area = " + Pi ' 4 * Pi/4, compare with estimate
<br/>
### `Function Rand:Int(minValue:Int, maxValue:Int = 1)`
Generate random integer
The optional parameter allows you to use [Rand](../../brl/brl.random/trandom/#method-rand-intminvalue-int-maxvalue-int-1) in 2 ways:
<table><tr><td> <b>Format</b></td><td><b>Result</b></td></tr><tr><td> &Rand(x)</td><td>Random integer in the range 1 to x (inclusive)</td></tr><tr><td> &Rand(x,y)</td><td>Random integer in the range x to y (inclusive)</table>
#### Returns
A random integer in the range min (inclusive) to max (inclusive)
#### Example
blitzmax ' Rand.bmx ' Toss a pair of dice. Result is in the range 1+1 to 6+6. ' Count how many times each result appears.
SuperStrict
Local count:Int[13]
For Local n:Int = 1 To 3600
Local toss:Int = Rand(1,6) + Rand(1,6)
count[toss] :+ 1
Next
For Local toss:Int = 2 To 12
Print LSet(toss, 5)+count[toss]
Next
<br/>
### `Function SeedRnd(seed:Int)`
Set random number generator seed
#### Example
blitzmax ' RndSeed.bmx and SeedRnd.bmx ( one example for both ) ' Get/Set random number seed.
SuperStrict
SeedRnd MilliSecs()
Local seed:Int = RndSeed()
Print "Initial seed="+seed
For Local k:Int = 1 To 10 Print Rand(10) Next
Print "Restoring seed"
SeedRnd seed
For Local k:Int = 1 To 10 Print Rand(10) Next
<br/>
### `Function RndSeed:Int()`
Get random number generator seed
Used in conjunction with SeedRnd, RndSeed allows you to reproduce sequences of random
numbers.
#### Returns
The current random number generator seed
#### Example
blitzmax ' RndSeed.bmx and SeedRnd.bmx ( one example for both ) ' Get/Set random number seed.
SuperStrict
SeedRnd MilliSecs()
local seed:int = RndSeed()
Print "Initial seed="+seed
For local k:int = 1 To 10
Print Rand(10)
Next
Print "Restoring seed"
SeedRnd seed
For local k:int = 1 To 10
Print Rand(10)
Next
```