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The Doctor Rostering Problem - Asser Fahrenholz

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Chapter 3. <strong>The</strong> model and design 11<br />

⎧<br />

⎪⎨ 1 if rule o is violated on<br />

yiko =<br />

⎪⎩<br />

0<br />

day i for doctor k<br />

otherwise<br />

⎧<br />

⎪⎨ 1 if rule 3 is violated on day i<br />

yijk3 =<br />

⎪⎩<br />

0<br />

shift j for doctor k<br />

otherwise<br />

⎧<br />

⎪⎨ 1 if the LHS of rule o is zero,<br />

tiko =<br />

⎪⎩<br />

0<br />

allows yiko to remain zero too<br />

otherwise<br />

⎧<br />

⎪⎨ 1 if the LHS of rule 3 is zero,<br />

tijk3 =<br />

⎪⎩<br />

0<br />

allows yijk3 to remain zero too<br />

otherwise<br />

<strong>The</strong> y-variables are used as counting variables, indicating how many violations of a soft<br />

constraint the doctor has. <strong>The</strong> t-variables are used for the specific case of the left hand<br />

side of the equation is zero. This variable, and the fact that we are dealing with a<br />

minimisation problem, allows the y-variable to remain zero.<br />

<strong>The</strong> following are the soft constraints that apply when constructing a model for the<br />

DRP:<br />

B0 No doctor should have both the Monday noon shift and the following Friday afternoon<br />

shift in the same week:<br />

min δB0<br />

<br />

i<br />

yik0<br />

<br />

∀ k<br />

st. xi2k + x (i+4)3k = 1 + yik0 − tik0<br />

∀ k, i ∈ M<br />

(B0)<br />

B1 No doctor should have both the Friday afternoon shift and the following Monday<br />

noon shift:<br />

min δB1<br />

<br />

i<br />

yik1<br />

<br />

∀ k<br />

st. xi3k + x (i+3)2k = 1 + yik1 − tik1<br />

∀ k, i ∈ F ∧ i < n − 3<br />

(B1)

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