Sizeof error and Z is a scalar/Vector but needs to be matrix

%           x   + y,     x >= 0 and y >= 0
%  f(x,y) = x   - y^2,   x >= 0 and y < 0 
%           -x^2 + y,    x < 0  and y >= 0
%           x^2 + y^2,   x < 0  and y < 0
%
% If x and y are vectors, then plot the 3D line.
% If x and y are matrices, then plot the surface.
% If x and y are 3 dimensions or more, then don't plot anything.

% Function Section
if size(x) == size(y)
    for n = 1:numel(x)
        if x(n) >= 0 && y(n) >=0
            z(n) = x(n) + y(n);
        end
        
        if x(n) >= 0 && y(n) < 0
            z(n) = x(n) - y(n)^2;
        end
        
        if x(n) < 0 && y(n) >= 0
            z(n) = -x(n)^2 + y(n);
        end
        
        if x(n) < 0 && y(n) < 0
            z(n) = x(n)^2 + y(n)^2;
        end
    end
else
    error('Inputs must be the same sized arrays')
end

% Plot Section
if isvector(x) && isvector(y)
    plot3(x,y,z)
end

if (ismatrix(x) && ismatrix(y))
    if numel(sizeof(x)) < 3 && numel(sizeof(y)) < 3 % Check if greater than or equal to three dim   <--Error
    surf(x,y,z)  %<--Error
    end
end

end

I am currently having trouble on the two labeled lines above, I am trying to plot a surface and make sure that the dimensions of the matrices are less than 3 but I am getting an error that z is a scalar/vector when it needs to be a matrix. As for the if statement above it the error is

Undefined function 'sizeof' for input arguments of type 'double'.

Error in MyEx08 (line 48)

if numel(sizeof(x)) < 3 && numel(sizeof(y)) < 3

The comments at the start of the code explain what I am trying to do.

Answer 1

[Fangjun Jiang]

sizeof() is not a function. Maybe you want to use ndims()

Answer 2

[Steven Lord]

x = 1:10;
if any(size(x) < 3)
    error('x has size less than 3 in at least one of its dimensions.')
end

Compare:

y = magic(5);
if any(size(y) < 3)
    error('y has size less than 3 in at least one of its dimensions.')
end

But I'd just preallocate z to be a zeros array the same size as x and y.

z = zeros(size(x));

Then you just have to check if z isvector or if it has size < 3 in any of its dimensions.

You may also be interested in this documentation page to avoid your for loop.