[R] parameter constraints with sem

[James Fowler]

I would like to constrain three of the parameters I am estimating using
sem (strucutral equation model package) but do not know how.
Specifically, I would like to use the following constraint:

beta1 + beta2 + beta3 = 1

can I assign variable names as the values for fixed parameters?  If so, I
could define the third parameter to be equal to 1 - beta1 - beta2.

thanks,
james


-------------------------------------------------------------------------
James H. Fowler, Assistant Professor   web:   http://jhfowler.ucdavis.edu
Department of Political Science        email: jhfowler at ucdavis.edu
University of California, Davis        phone: (530) 752-1649
One Shields Avenue                     fax:   (530) 752-8666
Davis, CA  95616