The Doctor Rostering Problem - Asser Fahrenholz
The Doctor Rostering Problem - Asser Fahrenholz
The Doctor Rostering Problem - Asser Fahrenholz
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Chapter 3. <strong>The</strong> model and design 13<br />
3.4 <strong>The</strong> objective function<br />
<strong>The</strong> constraints described in the two previous sections is the complete list of constraints<br />
as the medical practice has described them.<br />
<strong>The</strong> objective function value of a schedule s is the collective sum of the above described<br />
soft constraints and is denoted z(s):<br />
min z(s) = δB0<br />
+ δB2<br />
<br />
i<br />
⎛<br />
yik0<br />
⎝max<br />
k<br />
⎛<br />
+ δB3 ⎝ <br />
+ δB5<br />
+ δB6b<br />
i,j<br />
<br />
i<br />
<br />
i<br />
<br />
+ δB1<br />
i,j∈sa<br />
<br />
i<br />
yik1<br />
<br />
<br />
xijk − min<br />
k<br />
<br />
⎞ <br />
<br />
⎠ + δB4<br />
yijk3<br />
yik5<br />
<br />
yik6b<br />
+ δB6a<br />
<br />
i<br />
<br />
∀k<br />
i<br />
i,j∈sa<br />
yik4<br />
yik6a<br />
xijk<br />
<br />
<br />
⎞<br />
⎠<br />
(Z(S))<br />
An objective function value of 0 means that we have found an optimal solution for any<br />
DRP problem. If the objective function value is positive, it can still be optimal, but<br />
under any circumstances means that one or more soft constraints are invalid. Leaving<br />
the weight, δ, of all the soft constraints equal to 1 means that we can derive from an<br />
objective function value of i.e. 4, that soft constraints are invalid in 4 cases. If we<br />
choose to alter the weights of the rules, the same still applies, but the transparency of<br />
the objective function value decreases.<br />
<strong>The</strong> objective function thus determines the value of solutions for the DRP and is used<br />
by optimal solvers such as GAMS (see chapter 5) and the heuristics in the next chapter,<br />
which will describe how solutions can be found for the DRP.<br />
3.4.1 <strong>Problem</strong> size<br />
<strong>The</strong> amount of variables with 4 shifts per day, 6 doctors and 100 working days: