fix using 'nu' argument in n-d grid spline evaluator

csaps/_sspndg.py

@@ -107,12 +107,19 @@ def __call__(self,
             interpolation axis in the original array with the shape of x.
 
         """
+
         x = ndgrid_prepare_data_vectors(x, 'x', min_size=1)
 
         if len(x) != self.ndim:
             raise ValueError(
                 f"'x' sequence must have length {self.ndim} according to 'breaks'")
 
+        if nu is None:
+            nu = (0,) * len(x)
+
+        if extrapolate is None:
+            extrapolate = True
+
         shape = tuple(x.size for x in x)
 
         coeffs = ndg_coeffs_to_flatten(self.coeffs)
@@ -128,8 +135,9 @@ def __call__(self,
                 coeffs = coeffs.reshape(c_shape)
 
             coeffs_cnl = umv_coeffs_to_canonical(coeffs, self.pieces[i])
-            coeffs = PPoly.construct_fast(coeffs_cnl, self.breaks[i],
-                                          extrapolate=extrapolate, axis=1)(x[i])
+
+            spline = PPoly.construct_fast(coeffs_cnl, self.breaks[i], axis=1)
+            coeffs = spline(x[i], nu=nu[i], extrapolate=extrapolate)
 
             shape_r = (*coeffs_shape[:ndim_m1], shape[i])
             coeffs = coeffs.reshape(shape_r).transpose(permuted_axes)

tests/test_ndg.py

@@ -3,6 +3,7 @@
 import pytest
 
 import numpy as np
+from scipy.interpolate import NdPPoly
 import csaps
 
 
@@ -196,3 +197,29 @@ def test_auto_smooth_2d(ndgrid_2d_data):
 
     assert s.smooth == pytest.approx(smooth_expected)
     assert zi == pytest.approx(zi_expected)
+
+
+@pytest.mark.parametrize('nu', [
+    None,
+    (0, 0),
+    (1, 1),
+    (2, 2),
+])
+@pytest.mark.parametrize('extrapolate', [
+    None,
+    True,
+    False,
+])
+def test_evaluate_nu_extrapolate(nu: tuple, extrapolate: bool):
+    x = ([1, 2, 3, 4], [1, 2, 3, 4])
+    xi = ([0, 1, 2, 3, 4, 5], [0, 1, 2, 3, 4, 5])
+    y = np.arange(4 * 4).reshape((4, 4))
+
+    ss = csaps.NdGridCubicSmoothingSpline(x, y, smooth=1.0)
+    y_ss = ss(xi, nu=nu, extrapolate=extrapolate)
+
+    pp = NdPPoly(ss.spline.c, x)
+    xx = tuple(np.meshgrid(*xi, indexing='ij'))
+    y_pp = pp(xx, nu=nu, extrapolate=extrapolate)
+
+    np.testing.assert_allclose(y_ss, y_pp, rtol=1e-05, atol=1e-08, equal_nan=True)

tests/test_umv.py

@@ -241,3 +241,19 @@ def test_cubic_bc_natural():
 
     assert cs.c == pytest.approx(ss.spline.c)
     assert y_cs == pytest.approx(y_ss)
+
+
+@pytest.mark.parametrize('nu', [0, 1, 2])
+@pytest.mark.parametrize('extrapolate', [None, True, False, 'periodic'])
+def test_evaluate_nu_extrapolate(nu, extrapolate):
+    x = [1, 2, 3, 4]
+    xi = [0, 1, 2, 3, 4, 5]
+    y = [1, 2, 3, 4]
+
+    cs = CubicSpline(x, y)
+    y_cs = cs(xi, nu=nu, extrapolate=extrapolate)
+
+    ss = csaps.CubicSmoothingSpline(x, y, smooth=1.0)
+    y_ss = ss(xi, nu=nu, extrapolate=extrapolate)
+
+    np.testing.assert_allclose(y_ss, y_cs, rtol=1e-05, atol=1e-08, equal_nan=True)