# Placing Constraints on Constant Terms

#### Davis2010

##### New Member
I am running several iterations of a system of related equations. The first is four separate OLS equations estimating:

reg E_share lnp_cap lnp_lab lnp_energy lnp_mat
reg K_share lnp_cap lnp_lab lnp_energy lnp_mat
reg L_share lnp_cap lnp_lab lnp_energy lnp_mat
reg M_share lnp_cap lnp_lab lnp_energy lnp_mat

The second is a SUR regression of three of the four equations (the fourth is implicit):

sureg (eq1: E_share lnp_cap lnp_lab lnp_energy lnp_mat) (eq2: K_share lnp_cap lnp_lab lnp_energy lnp_mat) (eq3: L_share lnp_cap lnp_lab lnp_energy lnp_mat)

Finally, I would like to run a SUR regression as above, but with a constraint that the constants terms for all four equations sum to 1. I'm not sure what the syntax for this constraint is, as the variables I am imposing the constraint on are parameters and not actual variables in my data, and was wondering if someone has an idea of how to proceed. Thanks!

#### Etienne

##### New Member
Why don't you use the "constaint" command ? for instance :

constraint 1 : [eq1]_cons + [eq2]_cons + ... = 1
sureg ..., constaints(1)

This probably works...

#### Davis2010

##### New Member
Thanks for your help Etienne, that is very informative. One further question:
since the SUR only has 3 of our 4 equations (the fourth is redundant), how do I impose a constraint that the constants for all 4 equations sum to zero?

#### Etienne

##### New Member
Hi there,

Since your different equations contain exactly the same set of regressors on the right-hand-side, what you are doing is in fact equivalent to four separate OLS. However, I understand that you want to constrain the constants terms for all four equations to sum to 1. So my suggestion is :

constraint 1 : [eq1]_cons + ... + [eq4]_cons = 1
reg3 (eq1: y = ...) ... (eq4: y = ...) , constraints(1)

Hope this helps !