mpiexec

[A F]

OK guys, I am new to this mpiexec, so please help me as much as you can
I just installed mpich2 on a linux cluster. I was used to the mpich1.2.6.
Anyway, here is what i want to accomplish. Suppose I have a.out that needs 
to
run on 4 nodes, mach1, mach2, mach3, and mach4.
I want the rank in the communicator however to be mapping to physical nodes
as follows: (0->mach4) (1->mach3) (2->mach2) (3->mach1)
assume i have a file "hosts" that contains
mach1
mach2
mach3
mach4

>From what i understood from mpich2 documentation, i have to first do
mpd -n 4 -f hosts

then run mpiexec -n 4 a.out

well, how does mpiexec map the physical nodes to logical rank is this case?
does it assign logical ranks based on the host order as it appears in the 
hosts
file? If not, then How do i accomplish what i want?