Poloidal regridding according to prescribed Jacobian dependence
J ~ x^mx /(|grad psi|^npsi B^kb).
This a convenience routine typically used to remap the equilibrium onto
a grid with a different Jacobian dependence in x, |grad psi| and
the magnetic field B. Some codes will require a specific dependence,
among which
mx npsi kb
2 0 0 PEST1 coordinates
1 1 0 Equal Arc
0 0 0 Hamada
0 0 2 Boozer
are popular choices. For accuracy, the optimal choice may be equal-arc
as it prevents excessive bending of the poloidal rays on the outer board.
*NOTE* This routine does not rely on a XPLASMA/I2MEX representation.
It should typically be used BEFORE initializing the i2mex object.
integer, parameter :: r8 = selected_real_kind(12,100)
integer, intent(in) :: mx, npsi, kb the exponents entering the Jacobian
integer, intent(in) :: nt1, ns the poloidal/radial grid sizes
real(r8), intent(in) :: the(nt1), psi(ns) the poloidal [rad] and radial [Wb/rad] grids
real(r8), intent(in) :: g(ns) the covariant toroidal B function (Btor*X)
real(r8), intent(inout) :: x(nt1, ns), z(nt1,ns) old and new grid arrays
integer, intent(out) :: ier error flag