You don't. matlabFunction works on symbolic functions, not on MATLAB functions; you cannot call princomp from inside a pure symbolic formula (because it is not a MuPad routine) and you probably cannot pass princomp symbolic parameters.
MuPad (and Maple ) symbolic functions only ever return one value, but that one value might be an "expression sequence". If there are multiple left-hand-side variables on a MuPad ":=" assignment then the elements of the expression sequence get assigned to the corresponding output variable. If there is only one output variable, it gets assigned the entire expression sequence; if there is otherwise a mismatch between the number of output variables on the assigment and the number of elements in the expression sequence, there there will be an error generated.
A common trick to working with a MuPad function that returns an expression sequence is to include the entire expression inside of the list-building operators [] . For example, within MuPad,
f := () -> 18, 7, 23;
means that f is a function that takes no arguments and returns an expression sequence with 3 elements. You can get the list form of this via, e.g., R := [f()] which would return the list [18, 7, 23] and assign that to the variable R. You could then refer to the second output of f by referring to R[2]
