Error using * Inner matrix dimensions must agree - using meshplot

I have been trying to draw the direction fields of some first order differential equations and sometimes I can get it to work, others not.

This is an example of a problem I have just had:

To sketch the direction field of dy/dt - 2*y = t^2 . e^(2t)

I have tried the following:

>> [t y]=meshgrid(0:0.5:2,-4:0.5:4); >> dy=t.^2*exp(2.*t)+2.*y;

But an it immediately states there is an error: Error using * Inner matrix dimensions must agree.

I can't see what the problem is because in other instances this error does not occur. For example, this worked perfectly:

>> [t y]=meshgrid(-4:0.5:4,-4:0.5:4); >> dy=t - 3*y +exp(-2*t); >> dt=ones(size(dy)); >> L=sqrt(1+dy.^2); >> quiver (t, y, dt./L, dy./L, 0.5), axis tight;

Answer 1

[Mischa Kim]

Will, use

 [t y] = meshgrid(0:0.5:2,-4:0.5:4); 
 dy    = t.^2.*exp(2*t) + 2.*y;   % need to use dot operators all the way

 dt    = ones(size(dy));
 L     = sqrt(1 + dy.^2); 
 quiver (t, y, dt./L, dy./L, 0.5)
 axis tight;

[Will]

Thanks a lot, Mischa!