1874 ravel unravel index

parcels/_index_search.py

@@ -218,17 +218,14 @@ def _search_indices_rectilinear(
         _raise_field_sampling_error(z, y, x)
 
     if particle:
-        particle.xi[field.igrid] = xi
-        particle.yi[field.igrid] = yi
-        particle.zi[field.igrid] = zi
+        particle.ei[field.igrid] = field.ravel_index(xi, yi, zi)
 
     return (zeta, eta, xsi, zi, yi, xi)
 
 
 def _search_indices_curvilinear(field: Field, time, z, y, x, ti=-1, particle=None, search2D=False):
     if particle:
-        xi = particle.xi[field.igrid]
-        yi = particle.yi[field.igrid]
+        zi, yi, xi = field.unravel_index(particle.ei[field.igrid])
     else:
         xi = int(field.grid.xdim / 2) - 1
         yi = int(field.grid.ydim / 2) - 1
@@ -310,9 +307,7 @@ def _search_indices_curvilinear(field: Field, time, z, y, x, ti=-1, particle=Non
         _raise_field_sampling_error(z, y, x)
 
     if particle:
-        particle.xi[field.igrid] = xi
-        particle.yi[field.igrid] = yi
-        particle.zi[field.igrid] = zi
+        particle.ei[field.igrid] = field.ravel_index(xi, yi, zi)
 
     return (zeta, eta, xsi, zi, yi, xi)
 

parcels/application_kernels/advection.py

@@ -210,9 +210,7 @@
                 yi += 1
                 eta = 0
 
-    particle.xi[:] = xi
-    particle.yi[:] = yi
-    particle.zi[:] = zi
+    particle.ei[:] = fieldset.U.ravel_index(xi, yi, zi)
 
     grid = fieldset.U.grid
     if grid._gtype < 2:

parcels/field.py

@@ -1313,6 +1313,48 @@ def computeTimeChunk(self, data, tindex):
         self.filebuffers[tindex] = filebuffer
         return data
 
+    def ravel_index(self, xi, yi, zi):
+        """Return the flat index of the given grid points.
+
+        Parameters
+        ----------
+        xi : int
+            x index
+        yi : int
+            y index
+        zi : int
+            z index
+
+        Returns
+        -------
+        int
+            flat index
+        """
+        return xi + self.grid.xdim * (yi + self.grid.ydim * zi)
+
+    def unravel_index(self, ei):
+        """Return the xi, yi, zi indices for a given flat index.
+
+        Parameters
+        ----------
+        ei : int
+            The flat index to be unraveled.
+
+        Returns
+        -------
+        xi : int
+            The x index.
+        yi : int
+            The y index.
+        zi : int
+            The z index.
+        """
+        zi = ei // (self.grid.xdim * self.grid.ydim)
+        ei = ei % (self.grid.xdim * self.grid.ydim)
+        yi = ei // self.grid.xdim
+        xi = ei % self.grid.xdim
+        return zi, yi, xi
+
 
 class VectorField:
     """Class VectorField stores 2 or 3 fields which defines together a vector field.

parcels/particledata.py

@@ -122,7 +122,7 @@ def __init__(self, pclass, lon, lat, depth, time, lonlatdepth_dtype, pid_orig, n
         self._ncount = len(lon)
 
         for v in self.ptype.variables:
-            if v.name in ["xi", "yi", "zi", "ti"]:
+            if v.name in ["ei", "ti"]:
                 self._data[v.name] = np.empty((len(lon), ngrid), dtype=v.dtype)
             else:
                 self._data[v.name] = np.empty(self._ncount, dtype=v.dtype)

parcels/particleset.py

@@ -127,18 +127,13 @@
                     type(self).ngrids.initial = numgrids
                 self.ngrids = type(self).ngrids.initial
                 if self.ngrids >= 0:
-                    for index in ["xi", "yi", "zi", "ti"]:
-                        if index != "ti":
-                            setattr(self, index, np.zeros(self.ngrids, dtype=np.int32))
-                        else:
-                            setattr(self, index, -1 * np.ones(self.ngrids, dtype=np.int32))
+                    self.ei = np.zeros(self.ngrids, dtype=np.int32)
+                    self.ti = -1 * np.ones(self.ngrids, dtype=np.int32)
                 super(type(self), self).__init__(*args, **kwargs)
 
             array_class_vdict = {
                 "ngrids": Variable("ngrids", dtype=np.int32, to_write=False, initial=-1),
-                "xi": Variable("xi", dtype=np.int32, to_write=False),
-                "yi": Variable("yi", dtype=np.int32, to_write=False),
-                "zi": Variable("zi", dtype=np.int32, to_write=False),
+                "ei": Variable("ei", dtype=np.int32, to_write=False),
                 "ti": Variable("ti", dtype=np.int32, to_write=False, initial=-1),
                 "__init__": ArrayClass_init,
             }
@@ -436,7 +431,7 @@
 
     # TODO: This method is only tested in tutorial notebook. Add unit test?
     def populate_indices(self):
-        """Pre-populate guesses of particle xi/yi indices using a kdtree.
+        """Pre-populate guesses of particle ei (element id) indices using a kdtree.
 
         This is only intended for curvilinear grids, where the initial index search
         may be quite expensive.
@@ -454,10 +449,8 @@
             _, idx_nan = tree.query(pts.astype(tree_data.dtype))
 
             idx = np.where(IN)[0][idx_nan]
-            yi, xi = np.unravel_index(idx, grid.lon.shape)
 
-            self.particledata.data["xi"][:, i] = xi
-            self.particledata.data["yi"][:, i] = yi
+            self.particledata.data["ei"][:, i] = idx  # assumes that we are in the surface layer (zi=0)
 
     @classmethod
     def from_list(
@@ -725,9 +718,7 @@
             elif (
                 v.name
                 not in [
-                    "xi",
-                    "yi",
-                    "zi",
+                    "ei",
                     "ti",
                     "dt",
                     "depth",

tests/test_fieldset.py

@@ -570,7 +570,8 @@ def test_fieldset_write(tmp_zarrfile):
 
     def UpdateU(particle, fieldset, time):  # pragma: no cover
         tmp1, tmp2 = fieldset.UV[particle]
-        fieldset.U.data[particle.ti, particle.yi, particle.xi] += 1
+        _, yi, xi = fieldset.U.unravel_index(particle.ei)
+        fieldset.U.data[particle.ti, yi, xi] += 1
         fieldset.U.grid.time[0] = time
 
     pset = ParticleSet(fieldset, pclass=Particle, lon=5, lat=5)

tests/test_fieldset_sampling.py

@@ -131,7 +131,8 @@ def test_verticalsampling(zdir):
     fieldset = FieldSet.from_data(data, dimensions, mesh="flat")
     pset = ParticleSet(fieldset, pclass=Particle, lon=0, lat=0, depth=0.7 * zdir)
     pset.execute(AdvectionRK4, dt=1.0, runtime=1.0)
-    assert pset[0].zi == [2]
+    zi, yi, xi = fieldset.U.unravel_index(pset[0].ei)
+    assert zi == [2]
 
 
 def test_pset_from_field():

tests/test_grids.py

@@ -90,11 +90,14 @@ def sampleTemp(particle, fieldset, time):  # pragma: no cover
     pset.execute(AdvectionRK4 + pset.Kernel(sampleTemp), runtime=3, dt=1)
 
     # check if particle xi and yi are different for the two grids
-    # assert np.all([pset.xi[i, 0] != pset.xi[i, 1] for i in range(3)])
-    # assert np.all([pset.yi[i, 0] != pset.yi[i, 1] for i in range(3)])
-    assert np.all([pset[i].xi[0] != pset[i].xi[1] for i in range(3)])
-    assert np.all([pset[i].yi[0] != pset[i].yi[1] for i in range(3)])
-
+    # xi check from unraveled index
+    assert np.all(
+        [fieldset.U.unravel_index(pset[i].ei)[2][0] != fieldset.U.unravel_index(pset[i].ei)[2][1] for i in range(3)]
+    )
+    # yi check from unraveled index
+    assert np.all(
+        [fieldset.U.unravel_index(pset[i].ei)[1][0] != fieldset.U.unravel_index(pset[i].ei)[1][1] for i in range(3)]
+    )
     # advect without updating temperature to test particle deletion
     pset.remove_indices(np.array([1]))
     pset.execute(AdvectionRK4, runtime=1, dt=1)

tests/test_particlefile.py

@@ -273,9 +273,9 @@ def Get_XiYi(particle, fieldset, time):  # pragma: no cover
         and that the first outputted value is zero.
         Be careful when using multiple grids, as the index may be different for the grids.
         """
-        particle.pxi0 = particle.xi[0]
-        particle.pxi1 = particle.xi[1]
-        particle.pyi = particle.yi[0]
+        particle.pxi0 = fieldset.U.unravel_index(particle.ei[0])[2]
+        particle.pxi1 = fieldset.U.unravel_index(particle.ei[1])[2]
+        particle.pyi = fieldset.U.unravel_index(particle.ei[0])[1]
 
     def SampleP(particle, fieldset, time):  # pragma: no cover
         if time > 5 * 3600: