Passing a multi-variable function into quiver function

When I try to use the below code, I successfully plot a flow field, however, it is obviously wrong because there is no x-compononent of the field whatsoever and the y-component is constant throughout. I am pretty sure it has something to do with using a multivariable function in quiver, but I do not know how I would go about fixing this. Any help is appreciated. Thanks.

clear all;

[x,y] = meshgrid(-150:5:150,-150:5:150); % x and y values for velocity field
u = (-1.5*(x^2))-((1/3)*x^3); % u velocity function       
v = (3*x*y)+(y*x^2); % u velocity function      

figure;
quiver(x,y,u,v);
axis([-150 150 -150 150]); % fix axis to desired range
title({'Velocity and Streamline plots'}) % plot title

Answer 1

[DGM]

Maybe you meant this:

u = (-1.5*(x.^2))-((1/3)*x.^3); % u velocity function       
v = (3*x.*y)+(y.*x.^2); % u velocity function 

otherwise both u and v will be constant arrays

[Gavin Goddard]

Yes I did, thank you!