Added a new test.

tests/test_extrapolation.py

@@ -73,3 +73,36 @@ def test_partial_extrapolation(datafile):
     assert np.linalg.norm(guessed_density - density, ord=np.inf) < THRESHOLD
     assert np.linalg.norm(guessed_density - density, ord=np.inf) \
           /np.linalg.norm(density, ord=np.inf) < THRESHOLD
+
+@pytest.mark.parametrize("datafile", ["urea.json", "glucose.json"])
+def test_coefficient_extrapolation(datafile):
+
+    # load test data from json file
+    data = utils.load_json(f"tests/{datafile}")
+    nelectrons = data["nelectrons"]
+    natoms = data["trajectory"].shape[1]
+    nbasis = data["overlaps"].shape[1]
+    nframes = data["trajectory"].shape[0]
+
+    # amount of data we want to use for fitting
+    n = 9
+    assert n < nframes
+
+    # initialize an extrapolator
+    extrapolator = gext.Extrapolator(nelectrons, nbasis, natoms, nsteps=n)
+
+    # load data in the extrapolator up to index n - 1
+    for (coords, coeff, overlap) in zip(data["trajectory"][:n],
+            data["coefficients"][:n], data["overlaps"][:n]):
+        extrapolator.load_data(coords, coeff, overlap)
+
+    # check an extrapolation at index n
+    guessed_coefficients = extrapolator.guess_coefficients(
+        data["trajectory"][n], data["overlaps"][n])
+    coeff = data["coefficients"][n][:, :nelectrons//2]
+    density = coeff @ coeff.T
+    guessed_density = guessed_coefficients @ guessed_coefficients.T
+
+    assert np.linalg.norm(guessed_density - density, ord=np.inf) < THRESHOLD
+    assert np.linalg.norm(guessed_density - density, ord=np.inf) \
+          /np.linalg.norm(density, ord=np.inf) < THRESHOLD