# Generating uniform random numbers in Lua

## Generating uniform random numbers in Lua

You need to run `math.randomseed()`

**once** before using `math.random()`

, like this:

```
math.randomseed(os.time())
```

From your comment that you saw the first number is still the same. This is caused by the implementation of random generator in some platforms.

The solution is to pop some random numbers before using them for real:

```
math.randomseed(os.time())
math.random(); math.random(); math.random()
```

Note that the standard C library `random()`

is usually not so uniformly random, a better solution is to use a better random generator if your platform provides one.

Reference: Lua Math Library

Standard C random numbers generator used in Lua isnt guananteed to be good for simulation. The words Markov chain suggest that you may need a better one. Heres a generator widely used for Monte-Carlo calculations:

```
local A1, A2 = 727595, 798405 -- 5^17=D20*A1+A2
local D20, D40 = 1048576, 1099511627776 -- 2^20, 2^40
local X1, X2 = 0, 1
function rand()
local U = X2*A2
local V = (X1*A2 + X2*A1) % D20
V = (V*D20 + U) % D40
X1 = math.floor(V/D20)
X2 = V - X1*D20
return V/D40
end
```

It generates a number between 0 and 1, so `r = math.floor(rand()*10) + 1`

would go into your example.

(Thats multiplicative random number generator with period 2^38, multiplier 5^17 and modulo 2^40, original Pascal code by http://osmf.sscc.ru/~smp/)

#### Generating uniform random numbers in Lua

```
math.randomseed(os.clock()*100000000000)
for i=1,3 do
math.random(10000, 65000)
end
```

Always results in new random number. Changing seed value will ensure randomness, Dont follow `os.time()`

cuz its epoch time and changes after one second but `os.clock()`

dont have same value at any close instance. Cheers!