xj integer (for some or all j = 1,2,...,n). This problem is called the (linear) integer-programming problem. It is said to be a mixed integer program. when some, but not all, variables are restricted to be integer, and is called a pure integer program when all. decision variables must be integers. As we saw in the preceding chapter, if the constraints are of a network.
Anion gap: A measurement of the interval between the sum of routinely measured cations minus the sum of the routinely measured anions in the blood. The anion gap = (Na+ + K+) - (Cl- + HCO3-) where Na-is sodium, K+ is potassium, Cl-is chloride, and HCO3- is bicarbonate. The anion gap can be normal, high, or low.
The term anion gap usually implies  serum anion gap, but the urine anion gap is also a clinically useful measure.