Squeeze morph: Adding UCs tests

news/morphsqueeze.rst

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+**Added:**
+
+* Polynomial squeeze of x-axis of morphed data
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* <news item>
+
+**Security:**
+
+* <news item>

src/diffpy/morph/morphs/morphsqueeze.py

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+import numpy as np
+from numpy.polynomial import Polynomial
+from scipy.interpolate import CubicSpline
+
+from diffpy.morph.morphs.morph import LABEL_GR, LABEL_RA, Morph
+
+
+class MorphSqueeze(Morph):
+    """Apply a polynomial to squeeze the morph function. The morphed
+    data is returned on the same grid as the unmorphed data."""
+
+    # Define input output types
+    summary = "Squeeze morph by polynomial shift"
+    xinlabel = LABEL_RA
+    yinlabel = LABEL_GR
+    xoutlabel = LABEL_RA
+    youtlabel = LABEL_GR
+    parnames = ["squeeze"]
+
+    def morph(self, x_morph, y_morph, x_target, y_target):
+        """Squeeze the morph function.
+
+        This applies a polynomial to squeeze the morph non-linearly.
+
+        Configuration Variables
+        -----------------------
+        squeeze : list
+            The polynomial coefficients [a0, a1, ..., an] for the squeeze
+            function where the polynomial would be of the form
+            a0 + a1*x + a2*x^2 and so on.  The order of the polynomial is
+            determined by the length of the list.
+
+        Returns
+        -------
+            A tuple (x_morph_out, y_morph_out, x_target_out, y_target_out,
+            min_index, max_index) where the target values remain the same and
+            the morph data is shifted according to the squeeze. The morphed
+            data is returned on the same grid as the unmorphed data.
+            The min_index and max_index are the last index before the
+            interpolated region and the first index after the interpolated
+            region, respectively. If there is no extrapolation it returns None.
+
+        Example
+        -------
+        Import the squeeze morph function:
+        >>> from diffpy.morph.morphs.morphsqueeze import MorphSqueeze
+        Provide initial guess for squeezing coefficients:
+        >>> squeeze_coeff = [0.1, -0.01, 0.005]
+        Run the squeeze morph given input morph array (x_morph, y_morph)
+        and target array (x_target, y_target):
+        >>> morph = MorphSqueeze()
+        >>> morph.squeeze = squeeze_coeff
+        >>> x_morph_out, y_morph_out, x_target_out, y_target_out = morph(
+        ...     x_morph, y_morph, x_target, y_target)
+        To access parameters from the morph instance:
+        >>> x_morph_in = morph.x_morph_in
+        >>> y_morph_in = morph.y_morph_in
+        >>> x_target_in = morph.x_target_in
+        >>> y_target_in = morph.y_target_in
+        >>> squeeze_coeff_out = morph.squeeze
+        """
+        Morph.morph(self, x_morph, y_morph, x_target, y_target)
+
+        squeeze_polynomial = Polynomial(self.squeeze)
+        x_squeezed = self.x_morph_in + squeeze_polynomial(self.x_morph_in)
+        self.y_morph_out = CubicSpline(x_squeezed, self.y_morph_in)(
+            self.x_morph_in
+        )
+        left_extrap = np.where(self.x_morph_in < x_squeezed[0])[0]
+        right_extrap = np.where(self.x_morph_in > x_squeezed[-1])[0]
+        min_index = left_extrap[-1] if left_extrap.size else None
+        max_index = right_extrap[0] if right_extrap.size else None
+        return self.xyallout + (min_index, max_index)

tests/test_morphsqueeze.py

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+import numpy as np
+import pytest
+from numpy.polynomial import Polynomial
+
+from diffpy.morph.morphs.morphsqueeze import MorphSqueeze
+
+squeeze_coeffs_list = [
+    # The order of coefficients is [a0, a1, a2, ..., an]
+    # Negative cubic squeeze coefficients
+    [-0.2, -0.01, -0.001, -0.0001],
+    # Positive cubic squeeze coefficients
+    [0.2, 0.01, 0.001, 0.0001],
+    # Positive and negative cubic squeeze coefficients
+    [0.2, -0.01, 0.002, -0.0001],
+    # Quadratic squeeze coefficients
+    [-0.2, 0.005, -0.007],
+    # Linear squeeze coefficients
+    [0.1, 0.3],
+    # 4th order squeeze coefficients
+    [0.2, -0.01, 0.001, -0.001, 0.0004],
+    # Zeros and non-zeros, the full polynomial is applied
+    [0, 0.03, 0, -0.0001],
+    # Testing zeros, expect no squeezing
+    [0, 0, 0, 0, 0, 0],
+]
+morph_target_grids = [
+    # UCs from issue 181: https://github.com/diffpy/diffpy.morph/issues/181
+    # UC2: Same range and same grid density
+    (np.linspace(0, 10, 101), np.linspace(0, 10, 101)),
+    # UC4: Target range wider than morph, same grid density
+    (np.linspace(0, 10, 101), np.linspace(-2, 20, 221)),
+    # UC6: Target range wider than morph, target grid density finer than morph
+    (np.linspace(0, 10, 101), np.linspace(-2, 20, 421)),
+    # UC8: Target range wider than morph, morph grid density finer than target
+    (np.linspace(0, 10, 401), np.linspace(-2, 20, 200)),
+    # UC10: Morph range starts and ends earlier than target, same grid density
+    (np.linspace(-2, 10, 121), np.linspace(0, 20, 201)),
+    # UC12: Morph range wider than target, same grid density
+    (np.linspace(-2, 20, 221), np.linspace(0, 10, 101)),
+]
+
+
+@pytest.mark.parametrize("x_morph, x_target", morph_target_grids)
+@pytest.mark.parametrize("squeeze_coeffs", squeeze_coeffs_list)
+def test_morphsqueeze(x_morph, x_target, squeeze_coeffs):
+    y_target = np.sin(x_target)
+    squeeze_polynomial = Polynomial(squeeze_coeffs)
+    x_squeezed = x_morph + squeeze_polynomial(x_morph)
+    y_morph = np.sin(x_squeezed)
+    x_morph_expected = x_morph
+    y_morph_expected = np.sin(x_morph)
+    morph = MorphSqueeze()
+    morph.squeeze = squeeze_coeffs
+    (
+        x_morph_actual,
+        y_morph_actual,
+        x_target_actual,
+        y_target_actual,
+        low_extrap_idx,
+        high_extrap_idx,
+    ) = morph(x_morph, y_morph, x_target, y_target)
+    if low_extrap_idx is None and high_extrap_idx is None:
+        assert np.allclose(y_morph_actual, y_morph_expected, atol=1e-6)
+    else:
+        interp_start = low_extrap_idx + 1 if low_extrap_idx is not None else 0
+        interp_end = (
+            high_extrap_idx
+            if high_extrap_idx is not None
+            else len(y_morph_actual)
+        )
+        assert np.allclose(
+            y_morph_actual[interp_start:interp_end],
+            y_morph_expected[interp_start:interp_end],
+            atol=1e-6,
+        )
+    assert np.allclose(x_morph_actual, x_morph_expected)
+    assert np.allclose(x_target_actual, x_target)
+    assert np.allclose(y_target_actual, y_target)