Matlab-style short-circuit operation performed for operator & , Inline function, Fixed Point, Starting Point

Hello everybody, I'd appreciate if you help me to find out where the problem is.

I run the same code with different inline functions, for ones it works, but for this one I get the warning when running :

////////////////////inline function that doesn't work
  phi = inline('1-sin(2*x)', 'x') 
////////////////////the warning I get
  warning: Matlab-style short-circuit operation performed for operator &
  warning: called from
      fixpoint at line 22 column 9
  ans = Inf

//////////////////code itself
function [p,res,niter,inc]=fixpoint(phi, x0,tol,nmax,varargin)

c = x0; 
phix = feval(phi,c,varargin{:}); 
niter = 0; 
diff = tol+1;
while diff >= tol & niter <= nmax
   niter = niter + 1;
   diff = abs(phix - c);
   c = phix;
   phix = feval(phi,c,varargin{:});
end
if niter > nmax
    fprintf(['fixpoint stopped without converging to the desired tolerance',...
    'because the maximum number of iterations was reached\n']);
    varargin{:}
end
p = c;
res = phix - c;

return;

[Walter Roberson]

Please show a sample input.

Note: your code defines "inc" as an output but never assigns a value to it.