{ab, w, err} = NIntegrate`LobattoRuleData[num, 4]
(* {{0, 0.5000, 1.000}, {0.1667, 0.667, 0.1667}, {}} *)
{ab, w, err} = NIntegrate`LobattoRuleData[num, 4]
(* {{0, 0.5000, 1.000}, {0.1667, 0.667, 0.1667}, {}} *)
sys = Table[ (f[x] - x)* Sum[(Exp[2 - 2 f[x]]/(Exp[1 - f[x]] + Exp[1 - f[y]])^2 - Exp[1 - f[x]]/(Exp[1 - f[x]] + Exp[1 - f[y]]))* w[[Position[ab, y][[1, 1]]]], {y, ab}] + Sum[Exp[1 - f[x]]/(Exp[1 - f[x]] + Exp[1 - f[y]])* w[[Position[ab, y][[1, 1]]]], {y, ab}], {x, ab}];
sys = Table[
(f[x] - x)*
Sum[(Exp[2 - 2 f[x]]/(Exp[1 - f[x]] + Exp[1 - f[y]])^2 -
Exp[1 - f[x]]/(Exp[1 - f[x]] + Exp[1 - f[y]]))*
w[[Position[ab, y][[1, 1]]]], {y, ab}]
+
Sum[Exp[1 - f[x]]/(Exp[1 - f[x]] + Exp[1 - f[y]])*
w[[Position[ab, y][[1, 1]]]], {y, ab}], {x, ab}];
Now, create list of unknowns with some starting values:
vars = Table[{f[x], 2 + 1/2 x}, {x, ab}]
(* {{f[0], 2}, {f[0.5000], 2.2500}, {f[1.000], 2.5000}} *)
vars = Table[{f[x], 2 + 1/2 x}, {x, ab}]
(* {{f[0], 2}, {f[0.5000], 2.2500}, {f[1.000], 2.5000}} *)
FindRoot[sys, vars]
(* {f[0] -> 2.28088, f[0.5000] -> 2.51548, f[1.000] -> 2.78091} *)
.
FindRoot[sys, vars]
(* {f[0] -> 2.28088, f[0.5000] -> 2.51548, f[1.000] -> 2.78091} *)
f[x] = 2.28093 + 0.440941 x + 0.0538753 x^2 + 0.00521441 x^3 + 0.000168599 x^4
.
f[x] = 2.28093 + 0.440941 x + 0.0538753 x^2 + 0.00521441 x^3 +
0.000168599 x^4