[Ifeffit] Constraining phase composition

Hello, I have been fitting in Artemis three phases to my samples, that I denote x, y, and 1-(x+y). It often happens that x and y get unreasonable or negative values. How do I constrain x, y to be positive, and x+y < 1? On a side note, I have simple metallic lattices, and fitting two samples at the same time so have enough independent points. Best regards Olena Zavorotynska Sent from my Galaxy