🚀 go-pugleaf

Hi all,  my problem is with typesetting a ordinary sencond order 
differential equation in LaTeX, for which I typed in the source file the 
following lines:
	
	\boldmath
	\begin{equation}
		M_n \ddot{U}_{n} + C_n \dot{U}_{n} + K_n = F_n
	\end{equation}

To my supprise, the output is not what it should be --- the two dotted U_n
didn't come out right! The output of \ddot{U}_{n} is a hatted U_n. The 
output of \dot{U}_{n} is even stranger, it was U_n printed over by a 180deg 
rotated ")".

When I deleted the \boldmath, everything comes out fine. But I need to have 
the equation typesetted with boldface (but not the subscripts). I can use {\
bf...} inside the equation enviroment, the output are alright but the 
subcripts are also bold.

Can someone tell me what I did wrong?

Thanx in advance.


-gong