Analyzing Changes in Simultaneous right-hand Sides. When multiple bi valuesare changed simultaneously, the formula b * S * b can again be used to see how the right-hand sides change in the final tableau. If all these right-hand sides still are nonnegative, thefeasibility test will indicate that the revised solution provided by this tableau still is feasi-ble. Since row 0 has not changed, being feasible implies that this solution also is optimal.Although this approach works fine for checking the effect of a specific set of changes inthe ball, it does not give much insight into how far the ball can be simultaneously changed fromtheir original values before the revised solution will no longer be feasible. As part of postop-timality analysis, the management of an organization often is interested in investigating theeffect of various changes in policy decisions (e.g., the equivalent of resources being made avail-able to the activities under consideration) that determine the right-hand sides. Rather thanconsidering just one specific set of changes, management may want to explore the directions ofchanges where some right-hand sides increase while others decrease. Shadow prices are in-valuable for this kind of exploration. However, shadow prices remain valid for evaluating thethe effect of such changes on the Z only within certain ranges of changes. For each bi, the allowablerange to stay feasible gives this range if none of the other balls are changing at the same time.What do these allowable ranges become when some of the marbles are changing simultaneously?A partial answer to this question is provided by the following 100 percent rule, whichcombines the allowable changes (increase or decrease) for the individual Marbles that are givenby the last two columns of a table like Table 6.22.The 100 Percent Rule for Simultaneous Changes in right-hand Sides: Theshadow prices remain valid for predicting the effect of simultaneously changingthe right-hand sides of some of the functional constraints as long as the changesare not too large. To check whether the changes are small enough, calculate foreach change the percentage of the allowable change (increase or decrease) for thatright-hand side to remain within its allowable range to stay feasible. If the sum ofthe percentage changes does not exceed 100 percent, the shadow prices definitelywill still be valid. (If the sum does exceed 100 percent, then we cannot be sure.)Example (Variation 3 of the Wyndor Model). To illustrate this rule, consider Vari-ation 3 of the Wyndor Glass Co. model, which revises the original model by changing theright-hand side vector as follows:b b .The calculations for the 100 percent rule in this case areB2:12 15. Percentage of allowable increase 100 1561250%B3:18 15. Percentage of allowable decrease 100 1861550%Sum 100%Since the sum of 100 percent barely does not exceed 100 percent, the shadow pricesdefinitely are valid for predicting the effect of these changes on Z. In particular, since
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