BUG: preserve coefficients during inverse multiresolution analysis

pywt/_mra.py

@@ -280,7 +280,7 @@ def imra2(mra_coeffs):
         Statistical Association Vol. 92, No. 439 (Sep., 1997), pp. 868-880.
         https://doi.org/10.2307/2965551
     """
-    rec = mra_coeffs[0]
+    rec = mra_coeffs[0].copy()
     for j in range(1, len(mra_coeffs)):
         for n in range(3):
             rec += mra_coeffs[j][n]
@@ -427,7 +427,7 @@ def imran(mra_coeffs):
         Statistical Association Vol. 92, No. 439 (Sep., 1997), pp. 868-880.
         https://doi.org/10.2307/2965551
     """
-    rec = mra_coeffs[0]
+    rec = mra_coeffs[0].copy()
     for j in range(1, len(mra_coeffs)):
         for k, v in mra_coeffs[j].items():
             rec += v

pywt/tests/test_imra_preserves_coefficients.py

@@ -0,0 +1,32 @@
+import numpy as np
+import pytest
+from numpy.testing import assert_allclose, assert_array_equal
+
+import pywt
+
+
+@pytest.mark.parametrize('nd', [False, True])
+@pytest.mark.parametrize('stationary', [False, True])
+@pytest.mark.parametrize('readonly', [False, True])
+@pytest.mark.parametrize('dtype', ['float32', 'float64', 'complex64', 'complex128'])
+def test_inverse_mra_preserves_coefficients(nd, stationary, readonly, dtype):
+    x = np.arange(64).reshape(8, 8).astype(dtype)
+    if x.dtype.kind == 'c':
+        x.imag = x[::-1].real
+    forward, inverse = (pywt.mran, pywt.imran) if nd else (pywt.mra2, pywt.imra2)
+    transform = ('swt' if stationary else 'dwt') + ('n' if nd else '2')
+    coeffs = forward(x, 'db1', level=2, transform=transform)
+    arrays = [coeffs[0]]
+    for details in coeffs[1:]:
+        arrays.extend(details.values() if nd else details)
+    original = [a.copy() for a in arrays]
+    if readonly:
+        for a in arrays:
+            a.flags.writeable = False
+
+    first = inverse(coeffs)
+    for actual, expected in zip(arrays, original):
+        assert_array_equal(actual, expected)
+    second = inverse(coeffs)
+    assert_allclose(first, x, rtol=1e-5, atol=1e-5)
+    assert_array_equal(first, second)