This effect is documented... somewhere or other, I do not recall where. It occurs only in quite recent versions of MATLAB. It occurs because the JIT (Just In Time) compiler now gives priority to function calls to known routines, whereas before it gave priority to run-time assignments that are hidden with assignin().
syms is not a command: syms is a function. In its basic form, it is equivalent to
function syms(varargin)
for K = 1 : nargin
symname = varargin{K};
assignin('caller', symname, sym(symname));
end
end
It "poofs" variables into existence -- and MATLAB now gives priority to static analysis over dynamic analysis.
To avoid this problem, use
alpha = sym('alpha');
or any assignment to alpha before the syms call. For example,
alpha = [];
syms alpha
will do fine.
