Linear programming simplex - can I have a constraint with a multiplication? I'm not sure of this, can I have a constraint like this in a linear programming problem to be solved with simplex algorithm?
$$n_1t_1 + n_2t_2 > 200$$
where $n_1$ and $t_1$, $n_2$ and $t_2$ are different variables.
 A: It's non linear. It looks like separation of variables via substitution may work, introducing additional constraints, see p$15$ of: http://web.mit.edu/15.053/www/AMP-Chapter-13.pdf
A: This is an example of a quadratic (non-linear) constraint, and you can look up quadratically constrained quadratic programming (QCQP) e.g. on wikipedia if you want to learn more about how these kinds of problems with quadratic constraints and/or objectives are solved, although the computations are generally much slower and/or not guaranteed to find the best answer, in contrast to linear programming problems and algorithms.  This is because unlike linear programming, QCQP is NP-hard (very unlikely that any fast algorithm exists that is guaranteed to find the optimal solution).  Somebody else mentioned that you may be able to make substitutions and still use LP for some special situations similar to your example constraint, but if you have general quadratic constraints it won't always work, and you'll have to use QCQP instead of linear programming.
