Many thanks Rob. Your suggestion makes the program work properly, adding con link2 {al in FOOD}: diet[al] >= 1e-6*IsUsed[al]; I obtain: [1] diet IsUsed Bread 0.000000 0 Cheese 0.449499 1 Fish 0.500000 1 Milk 0.053599 1 Potato 1.865168 1 Yogurt 0.000000 0 Best regards.
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