Try to make splines more periodic

The RectBivariateSpline does not support periodic data, but by including
copies on the left and on the right, the spline will be closer to periodic.

zoidberg/poloidal_grid.py

@@ -293,10 +293,10 @@ def __init__(self, R, Z):
         self.nz = nz
 
         xinds = np.arange(nx)
-        zinds = np.arange(nz + 1)
+        zinds = np.arange(nz * 3)
         # Repeat the final point in y since periodic in y
-        R_ext = np.concatenate((R, np.reshape(R[:, 0], (nx, 1))), axis=1)
-        Z_ext = np.concatenate((Z, np.reshape(Z[:, 0], (nx, 1))), axis=1)
+        R_ext = np.concatenate((R, R, R), axis=1)
+        Z_ext = np.concatenate((Z, Z, Z), axis=1)
 
         self._spl_r = RectBivariateSpline(xinds, zinds, R_ext)
         self._spl_z = RectBivariateSpline(xinds, zinds, Z_ext)
@@ -330,8 +330,8 @@ def getCoordinate(self, xind, zind, dx=0, dz=0):
         # Periodic in y
         zind = np.remainder(zind, nz)
 
-        R = self._spl_r(xind, zind, dx=dx, dy=dz, grid=False)
-        Z = self._spl_z(xind, zind, dx=dx, dy=dz, grid=False)
+        R = self._spl_r(xind, zind + self.nz, dx=dx, dy=dz, grid=False)
+        Z = self._spl_z(xind, zind + self.nz, dx=dx, dy=dz, grid=False)
 
         return R, Z