What is a unique optimal solution?
Regarding this, what is an optimal solution?
An optimal solution is a feasible solution where the objective function reaches its maximum (or minimum) value – for example, the most profit or the least cost. A globally optimal solution is one where there are no other feasible solutions with better objective function values.
Keeping this in consideration, what is the difference between feasible solution and optimal solution?
A feasible solution is a set of values for the decision variables that satisfies all of the constraints in an optimization problem. A local optimal solution is one where there is no other feasible solution "in the vicinity" with a better objective function value.
In linear programming we have a set of linear inequalities expressed in variables and a linear function we wish to minimise or maximise, expressed in the same variables. If the inequalities contradict each other, we might end up with an empty region, which implies that there is no 'optimal' solution.