Dear statalist members,

I used nlsur command to estimate 3 different equations by using panel data, but I got some zero coefficient values and (constrained) standard errors.
Could you tell me how should I interpret these results and solve this problem?

Here is the code I used:
nlsur (Price = {c0}+{c1}*q_hat+{c2}*d_stock_hat+{c3}*Tariff+{c4}* Year) ///
(lcon = {b0}+{a1}*lP_hat+{a2}*lpv_usd+{a3}*lpvo_usd+{a4}*l st_hat+{a5}*lsto) ///
(k_new = {c1}*d_q_t1_hat + {c2}*d2_stock_t1_hat+{c3}*d_tariff_t1+ exp({b0}*P_hat^{a1}*Price_volatility_usd^{a2}*Pric e_volatility_others_usd^{a3}*stock_hat^{a4}*Stock_ others^{a5})+{c4}), vce(cluster pan_id) nolog


Results:
------------------------------------------------------------------------------
| Robust
| Coef. Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
/c0 | 0 (constrained)
/c1 | -2.86e-06 7.87e-07 -3.64 0.000 -4.40e-06 -1.32e-06
/c2 | .0000368 .0000182 2.02 0.044 1.05e-06 .0000725
/c3 | 0 (constrained)
/c4 | .3479641 .0418792 8.31 0.000 .2658824 .4300458
/b0 | 5.113244 .1122169 45.57 0.000 4.893303 5.333185
/a1 | .0839221 .0100496 8.35 0.000 .0642253 .1036189
/a2 | .0391057 .0168705 2.32 0.020 .0060402 .0721712
/a3 | -.08336 .0289692 -2.88 0.004 -.1401385 -.0265815
/a4 | -.0200906 .0056341 -3.57 0.000 -.0311333 -.0090479
/a5 | -.0008483 .0026532 -0.32 0.749 -.0060485 .0043519
------------------------------------------------------------------------------

Thank you very much in advance.