set PROD;
set SOST;

param cost_unit{PROD}>0;
param quant_min{SOST}>=0;
param quant_unit{SOST,PROD}>0;

var x{PROD} >= 0;

subject to min_sostanza{i in SOST} : sum{j in PROD} quant_unit[i,j]*x[j] >= quant_min[i];

minimize total_cost : sum{j in PROD} cost_unit[j]*x[j];