Why does changing the order of my multiplication yield different graphs?

I was doing an activity where I had to use parametric equations to graph the surface formed by revolving the curve about the x-axis. I first did it like this:

>> u=linspace(0,1,50);

>>v=linspace(0,2*pi,50);

>>[U,V]=meshgrid(u,v);

>>X=(3*(U-1/3).^2)*cos(V);

>>Y=(3*(U-1/3).^2)*sin(V);

>>Z=U;

>> surf(X,Y,Z)

And got the strange graph, with very strange bounds:

When I switched the order of multiplication in the X and Y parametric equations, to put the trig first:

>> u=linspace(0,1,50);

>>v=linspace(0,2*pi,50);

>>[U,V]=meshgrid(u,v);

>>X=cos(V)*(3*(U-1/3).^2);

>>Y=sin(V)*(3*(U-1/3).^2);

>>Z=U;

>>surf(X,Y,Z)

The graph was exactly what I was looking for:

Can anybody help me understand why the order of multiplication gives me a different result? Thanks.

Answer 1

[madhan ravi]

a*b~=b*a % don‘t forget the rules of matrix multiplication

change * to .* element wise operation you will get the same result

[Brad Smith]

Thanks! That makes perfect sense. I wasn't thinking about that.

[madhan ravi]

Anytime :) , make sure to accept the answer if it helped you