grad_2d Subroutine

public subroutine grad_2d(x, y, u, dudx, dudy, undef)

Calculate gradient of "u" in two dimensions based on the 2nd order central differential approximation:
$\frac{\partial u}{\partial x}\approx \frac{u_{i+1}-u_{i-1}}{2dx}$ $\nabla u\approx \left(\frac{p_{i+1,j}-p_{i-1,j}}{2dx} ,\; \frac{p_{i,j+1}-p_{i,j-1}}{2dy} \right)$

Arguments

Type	Intent	Optional	Attributes		Name
double precision,	intent(in)			::	x(:)	Axis point 1
double precision,	intent(in)			::	y(:)	Axis point 2
double precision,	intent(in)			::	u(size(x),size(y))
double precision,	intent(out)			::	dudx(size(x),size(y))
double precision,	intent(out)			::	dudy(size(x),size(y))
double precision,	intent(in),	optional		::	undef