180 instances with service cost (Cjτ), defining service cost as total cost (operation and maintenance costs) of maintaining machine j that has not been maintained in τ periods. Each file contains a matrix of the service costs Cjt where the rows represent the machines (j) and the columns the number of periods since the last revision (τ) Service cost is composed by linear operating cost (aj· τ) and step function maintenance cost (cfjτ) both depending on the number of periods (τ) since last maintenance of machine j was executed