Description 
GENDIST  generate random numbers according to a discrete probability distribution
Tristan Ursell, 2011.
T = gendist(P,N,M)
T = gendist(P,N,M,'plot')
The function gendist(P,N,M) takes in a positive vector P whose values form a discrete probability distribution for the indices of P. The function outputs an N x M matrix of integers corresponding to the indices of P chosen at random from the given underlying distribution.
P will be normalized, if it is not normalized already. Both N and M must be greater than or equal to 1. The optional parameter 'plot' creates a plot displaying the input distribution in red and the generated points as a blue histogram.
Conceptual EXAMPLE:
If P = [0.2 0.4 0.4] (note sum(P)=1), then T can only take on values of 1, 2 or 3, corresponding to the possible indices of P. If one calls gendist(P,1,10), then on average the output T should contain two 1's, four 2's and four 3's, in accordance with the values of P, and a possible output might look like:
T = gendist(P,1,10)
T = 2 2 2 3 3 3 1 3 1 3
If, for example, P is a probability distribution for position, with positions X = [5 10 15] (does not have to be linearly spaced), then the set of generated positions is X(T).
EXAMPLE 1:
P = rand(1,50);
T = gendist(P,100,1000,'plot');
EXAMPLE 2:
X = 3:0.1:3;
P = 1+sin(X);
T = gendist(P,100,1000,'plot');
Xrand = X(T);
