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The Doctor Rostering Problem - Asser Fahrenholz

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Chapter 3. <strong>The</strong> model and design 10<br />

H0 No doctor may take two shifts in a row:<br />

xijk + x i(j+1)k ≤ 1 ∀ i, j = {1, 2, 3}, k (H0)<br />

H1 After an evening shift, a doctor cannot have a noon shift on the following day:<br />

bi4k + x (i+1)2k ≤ 1 ∀ i = {1 . . . n − 1}, k (H1)<br />

H2 Following a night shift, a doctor cannot have a noon shift nor an afternoon shift:<br />

bi1k + xi2k + xi3k ≤ 1 ∀ i, k (H2)<br />

H3a <strong>Doctor</strong>s having a shift outside the house cannot have one in the house simultane-<br />

ously:<br />

H3b Requests for a shift off must be granted:<br />

H4 Demands must be met:<br />

xijk + bijk ≤ 1 ∀ i, j, k (H3a)<br />

xijk + cijk ≤ 1 ∀ i, j, k (H3b)<br />

m<br />

xijk = 1 + sij ∀ i, j (H4)<br />

k=1<br />

H5 No afternoon shift before an evening shift:<br />

3.3 Soft constraints<br />

xi3k + bi4k ≤ 1 ∀ i, k (H5)<br />

<strong>The</strong> soft constraints does not require validity for the solution to be feasible, though the<br />

quality of the solution improves the fewer soft constraints are invalid. Soft constraints are<br />

commonly modelled in the evaluation or objective function, as a sum of the penalties<br />

that arise when not satisfying the individual constraints. Each soft constraint has a<br />

weight δ attached, allowing the user to prioritise certain constraints over others.<br />

I now introduce the following variables:

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