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Q2 Z2,(Q2) Z2(Q2) - Institute for Water Resources - U.S. Army

Q2 Z2,(Q2) Z2(Q2) - Institute for Water Resources - U.S. Army

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-X<br />

_21<br />

5.15<br />

L4.45<br />

TRUCK<br />

RAIL<br />

lalm■•••<br />

DIAGRAM 1<br />

AREA<br />

BARGE AREA<br />

7.89 8.59 -X 31<br />

Given equation (36) it is also possible to draw the boundaries<br />

of the three decision regions on the X 31 X21 plane, as was done in Diagram 1.<br />

We can now compute theprobabilities that each mode will be chosen<br />

at a.particular shipment point by using equation (25) <strong>for</strong> P 1 (X), and the<br />

corresponding equations <strong>for</strong> P 2 (X), and P 3(X). Let us compute an example,<br />

assuming that X31 = -lo<br />

--' -21<br />

weighed set of rules,<br />

6, and X 32 = -4. Then, <strong>for</strong> the January<br />

• n 3 (X31 ) n (X )<br />

2 21<br />

n 3 (X32 )<br />

in " -1.412, in _<br />

=<br />

r. • 797 . in<br />

n<br />

= -.126.<br />

1 21<br />

(X<br />

2 32<br />

).<br />

The inverse of these ratios are identical except <strong>for</strong> the sign. It follows that<br />

1 1<br />

P (X) - .591 P<br />

1 2<br />

(X) = - .244<br />

1 + e -1.412 + e -.797<br />

1 + e -.126 + e .797<br />

1<br />

P 3 (X) - .161.<br />

1 + e 1.412 + e .126<br />

P 1 (X) + P 2 (X) + P 3 (X) = .591 + .244 + .161 = .996, which is very close to 1.<br />

As the probability that barge will be chosen is .591, one should classify this<br />

origin as a barge origin. Note that if the probabilities were used to classify<br />

52

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