[R] questions about optim

[Dean Lee]

Hi,
I am trying to do parameter estimation with optim, but I can't get it to 
work quite right-- I have an equation X = Y where X is a gaussian, Y is a 
multinomial distribution, and I am trying to estimate the probabilities of 
Y( the mean and sd of X are known ), Theta1, Theta2, Theta3, and Theta4; I 
do not know how I can specify the constraint that Theta1 + Theta2 + Theta3 + 
Theta4 = 1 in optim. Is there another method/package that I should use for 
this?
Also, I wonder if there's a more elegant way to code this equation in R; 
right now my function looks something like Y/rnorm( 10000, mean, sd), and I 
try to maximize it to 1; is it possible to "plug" the entire gaussian( 
instead of using rnorm ) into the equation? Thanks.

Regards,

-Dean