@conference{disney2019,
  author       = {S.M. Disney},
  title        = {Discrete control theory},
  booktitle    = {The spectrum of systems approaches to problem solving - from systems engineering to systems dynamics to systems thinking. A workshop hosted by the UK Chapter of the Systems Dynamics Society and the EPSRC ReRun project},
  year         = {2019},
  address      = {Cardiff, UK},
  month        = {22nd March},
  abstract     = {Using block diagrams, z-transforms and Tsypkin’s relation I show how to obtain the variances of the orders and inventory levels maintained by the proportional order-up-to policy. Assuming demand is uncorrelated and normally distributed, a proportional feedback controller equal to the golden ratio minimizes a weighted sum of the variances. One may also minimize the inventory and capacity costs maintained by this replenishment policy.}
  }