# How can I generate random variates from a from a PDF that I have defined?

My problem is that Pick evaluates all the elements of a list at once. In my code I need a similar function that evaluates each element of a list. I need to generate 1000000 numbers for a PDF.

My code is:

n = 1000000;
yteste = RandomReal[{0, 2/3}, 2 n];
xteste = RandomReal[{-1, 1}, 2 n];

f[x_] := 2/3 (1 - Abs[x]^3)

If[Length[xaceitos] <= n,
AppendTo[xaceitos, Pick[xteste, UnitStep[f[xteste] - yteste], 1]],
Nothing]


Is there any other function that can do it?

• Can you explain what you want your code to produce? What is the expected form of xaceitos, for instance? – J. M. will be back soon Sep 25 '18 at 18:42
• I need to generate n numbers that follow the PDF f[x], this is the monte carlo Method. The problem is, when i use the rejection method i only receive less than n numbers. I need to receive exactly n numbers. – Hugo David Costa Pereira Sep 25 '18 at 18:45
• That is slightly clearer, but only a little. So, you want to sample under the curve of f[x] for Abs[x] < 1? If so: dist = ProbabilityDistribution[f[x], {x, -1, 1}]; xaceitos = RandomVariate[dist, n]; Show[Histogram[xaceitos, Automatic, "PDF"], Plot[f[x], {x, -1, 1}]] – J. M. will be back soon Sep 25 '18 at 18:48
• Yes, exactly. The curve of the histogram[xaceitos] must have the same shape o f[x]. – Hugo David Costa Pereira Sep 25 '18 at 18:50

As @JM says, just use ProbabilityDistribution:

dist = ProbabilityDistribution[f[x], {x, -1, 1}];

random = RandomVariate[dist, 10^6];
Length[random]


1000000

Visualization:

Histogram[random, Automatic, "PDF"]