I am working on the follwoing nonlinear model.
x $\leq$ 3
When I solve this problem on LINGO, I got the message "dual solution does not exist but primal solution will be shown". 1) Why there is no dual solution? How can I prove it ? How can I prove that there is no dual solution ?
2) How can we interpret all this case , I mean there is no solution for dual problem but there is only for primal solution.
Thank you in advance