convolution of the double exponential distribution

Is there any R function that computes the convolution of the double
exponential distribution?

If not, is there a good way to integrate ((q+x)^n)*exp(-2x) over x from
0 to Inf for any value of q and for any positive integer n? I need to
perform the integration within a function with q and n as arguments. The
function integrate() is giving me this message:

"evaluation of function gave a result of wrong length"

David
_______________________________________
David R. Bickel  http://davidbickel.com
Research Scientist
Pioneer Hi-Bred International (DuPont)
Bioinformatics and Exploratory Research
7200 NW 62nd Ave.; PO Box 184
Johnston, IA 50131-0184
515-334-4739 Tel
515-334-4473 Fax
david.bickel at pioneer.com, bickel at prueba.info

This communication is for use by the intended recipient and ...{{dropped}}