[Solved] Non-scalar in Uniform output error in arrayfun. How to fix?

Question

The error message give you a big hint where to look:

Undefined operator ‘+’ for input arguments of type ‘cell’.

Error in gbp2/pts (line 36)
ylist(z) = ylist(z) + arrayfun(@(coor) u(z, coor, mode, w, R,
Psi),xlist(z).’,’uniformoutput’,false);

From the documentation for arrayfun and the 'UniformOutput' option:

Requests that the arrayfun function combine the outputs into cell arrays B1,…,Bm. The outputs of function func can be of any size or type.

Indeed, if you check, the output of this line is a cell array:

arrayfun(@(coor) u(z, coor, mode, w, R, Psi),xlist(z),'uniformoutput',false)

You can’t sum the values from the cell array directly. Here’s one of several ways you can do this:

v = arrayfun(@(coor) u(z, coor, mode, w, R, Psi),xlist(z),'uniformoutput',false);
ylist(z) = ylist(z) + [v{:}];

However, I don’t see why you need to used the 'UniformOutput' option or even the slow arrayfun at all. Just vectorize your function with respect to coor:

u = @(z, coor, mode, w, R, Psi)(2/pi)^(1/4)*sqrt(exp(1i*(2*mode+1)*Psi)/(2^mode*factorial(mode)*w))*...
        hermiteH(mode,sqrt(2)*coor/w).*exp(-coor.^2*(1/w^2+1i*k/(2*R))-1i*k*z);

Now

ylist(z) = ylist(z) + u(z, xlist(z), mode, w, R, Psi);

Some additional suggestions: Don’t use global variables – they’re inefficient and there are almost always better solutions. If pts is meant to be a nested function, you’re missing a closing end for the main gbp2 function. It might be a good idea to rename your variable mode so that it doesn’t overload the built-in function of the same name. Psif isn’t defined. And zeros(1,size(xlist(z),2)) can be written simply as zeros(size(xlist(z))).

Accepted Answer