R help - Feb 2011 - regsubsets {leaps}

Hi, 

I'd like to run regsubsets for model selection by exhaustive search. I have
a list with 20 potential explanatory variables, which represent the real and
the imaginary parts of 10 "kinds" of complex numbers:

x <- list(r1=r1, r2=r2, r3=r3, ..., r10=r10, i1=i1, i2=i2, i3=i3, ...,
i10=i10)

Is there an easy way to constrain the model search so that "r"s and
"i"s are
treated as pairs that should always appear together in the models? i.e., in
a way where only models like these:

y ~ r1, i1 
y ~ r3, i3, r8, i8
y ~ r1, i1, r4, i4, r5, i5

are considered in the search, and models like the ones below are not:

y ~ r1, i8
y ~ r1, r3
y ~  r9, i5, i7

Sorry if this isn't very clear! 

Thanks
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I've tried grouping the real and imaginary parts as a single complex number,
e.g.
> z1 <- complex(real=r1, imaginary=i1)
Although complex variables are not allowed in lm, I can run regsubsets just
fine:
> z <- cbind(z1, z2, z3, ..., z10)
> bestsubs <- regsubsets(z, y, nbest=1, nvmax=5, intercept=T,
> method="exhaustive", names=dimnames(x)[2])
The problem is that the code is using only one coefficient for each
"z"
(probably for the amplitude), and not one for the real part and one for the
imaginary part, as I'd like to.
> coef(bestsubs,3)
(Intercept)         z1         z3         z4 
 -397.43425   -35.86687   202.20521   716.02103 

Any suggestions?

Thanks
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