Easy enough to type out, but so what. What do you want to do with m? Show it as an image or a surface or something? What range do you want for x and y?
xlin = linspace(-5, 5, numPoints);
ylin = linspace(-8, 8, numPoints);
[x, y] = meshgrid(xlin, ylin);
m = 2*x.^3-2*y-sqrt(x-y.^3)./(1+(x-y)./(x.^2+3))+sin(x./y*pi)+exp(y/3);
xlabel('x', 'FontSize', fontSize);
ylabel('y', 'FontSize', fontSize);
surf(x, y, m, 'EdgeColor', 'none');
xlabel('x', 'FontSize', fontSize);
ylabel('y', 'FontSize', fontSize);
zlabel('m', 'FontSize', fontSize);