I am working with a 2D vector field for velocity in the $xy$-coordinate plane. Given
$$v(x,y) = i_x * x - i_y * y$$
where $v$ denotes velocity and $i_x$ and $i_y$ are the unit vectors $(1,0)$ and $(0,1)$ respectively, how do I find the acceleration $a(x,y)$? I know that the traditional vector function has its' $x$ and $y$ components as functions of time $t$, but the functions $x(t)$ and $y(t)$ are not available.