(* Discounts on Purchase Price and Freight Costs *);



demand = 3000; holding = 0.2; setup = 700;

price = PWSFreeze[

      PWS[

        {{{1, 1500}, 20 &}, {{IA[1500], 4000}, 19 &},

          {{IA[4000], Infinity}, 18.5 &}}

        ]];

purchase = demand setup/# & + demand price + (holding #/2 &) price;

tariff1 = Table[{{IA[400(j - 1)], 400j},

          Evaluate[400j (1 - 0.02(j - 1))] &},

        {j, 25}] /. IA[0] -> 1;

tariff2 = Table[{{IA[10000 + 400(j - 1)], 10000 + 400j},

        Evaluate[5200 + 8j] &},

      {j, 10}];

tariff = PWSFreeze[PWS[Join[tariff1, tariff2]]];

totalCost = purchase + (demand/# &) tariff;

Plot[totalCost[q], {q, 1, 5600},

    AxesLabel -> {"Quantity", "Cost"},

    PlotStyle -> {{}, {Dashing[{0.01}]}},

    PlotRange -> {60000, 74000}];



Plot[totalCost[q], {q, 200, 1800},

    AxesLabel -> {"Quantity", "Cost"},

    PlotStyle -> {{}, {Dashing[{0.01}]}},

    PlotRange -> {63000, 70000}];

FindMinimum[totalCost[q], {q}]