I have a piecewise function that has as one piece the result of a numerical approximation, like in the example below: Y = 1; a = 1; b = 0.9; alphalowx = a*Log[a + b]; alphahighx = Y + a*Log[a + b] – (a + b – 1); f1[x_?NumericQ] := Piecewise[{{0, x <= alphalowx}, {xRead more