Joint probability density function of complex numbers in Matlab

Hi everybody,

I want to calculate the transition probability matrix of an AWGN channel (with complex QAM symbols). The input X is a row of discrete complex numbers and the output Y is a row of continuous complex numbers. Does somebody know how to compute that in Matlab? I suppose I should calculate the joint probability density function of X and Y. My problem is not only X and Y are complex, but also X is discrete and Y is continuous.

I would be very grateful if somebody help me.