Mathematica：使用许多函数操作ContourPlot3D错误

Question

我正在尝试操作三个功能，并选择弹出菜单，它将显示哪些功能。我还没有放置变量（它们将代替16,25,2等）。

出于某种原因，当我运行它时，它会返回带有弹出菜单的Manipulate框，但不显示ContourPlot3D，而是显示其代码。你能找到错误吗？

Clear[x, y, z, ell, mu, du]

ell[x_, y_, z_] := x^2/16 + y^2/25 + z^2/2
mu[x_, y_, z_] := x^2/1 + y^2/2 - z^2/1
du[x_, y_, z_] := x^2/2 - y^2/4 - z^2/1

Manipulate[
 ContourPlot3D[
  F == 1, {x, -4, 4}, {y, -5, 5}, {z, -3, 3}], {F, {ell, mu, du}, ControlType -> PopupMenu}]

这是mathematica文档中的示例：

Manipulate[Plot[f[x], {x, 0, 2 Pi}], {f, {Sin, Cos, Tan, Cot}, ControlType -> PopupMenu}]

Answer 1

单步：

 f["ell"][x_, y_, z_] := x^2/16 + y^2/25 + z^2/2
 f["mu"][x_, y_, z_] := x^2/1 + y^2/2 - z^2/1
 f["du"][x_, y_, z_] := x^2/2 - y^2/4 - z^2/1
 Manipulate[
     ContourPlot3D[
          f[key][x, y, z] == 1, {x, -4, 4}, {y, -5, 5}, {z, -3, 3}],
                {{key,"ell"}, {"ell", "mu", "du"}, ControlType -> PopupMenu}]