A modified version of pbivnorm() from package pbivnorm
.
It is needed in the imputation routine for rounded income.
pbivnormX(x, y, rho = 0)
the vector (or a two columned matrix) with the values of the first random variable
the vector with the values of the second random variable
the correlation (a scalar) between the two random variables.
A vector with the values of the density distribution at the points (x, y).