numpy · eric-wieser · Jul 31, 2018 · Jul 20, 2018 · Jul 20, 2018 · Jul 20, 2018
diff --git a/doc/release/1.16.0-notes.rst b/doc/release/1.16.0-notes.rst
@@ -47,6 +47,12 @@ Even when no elements needed to be drawn, ``np.random.randint`` and
 distribution. This has been fixed so that e.g.
 ``np.random.choice([], 0) == np.array([], dtype=float64)``.
 
+``linalg.qr`` now works with empty matrices
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Previously, a ``LinAlgError`` would be raised when empty matrix
+(with zero rows and/or columns) is passed in. This has been fixed
+so that outputs of appropriate shapes are returned for the various modes.
+
 ARM support updated
 -------------------
 Support for ARM CPUs has been updated to accommodate 32 and 64 bit targets,

diff --git a/numpy/linalg/linalg.py b/numpy/linalg/linalg.py
@@ -858,13 +858,13 @@ def qr(a, mode='reduced'):
 
     a, wrap = _makearray(a)
     _assertRank2(a)
-    _assertNoEmpty2d(a)
     m, n = a.shape
     t, result_t = _commonType(a)
     a = _fastCopyAndTranspose(t, a)
     a = _to_native_byte_order(a)
     mn = min(m, n)
     tau = zeros((mn,), t)
+
     if isComplexType(t):
         lapack_routine = lapack_lite.zgeqrf
         routine_name = 'zgeqrf'
@@ -875,14 +875,14 @@ def qr(a, mode='reduced'):
     # calculate optimal size of work data 'work'
     lwork = 1
     work = zeros((lwork,), t)
-    results = lapack_routine(m, n, a, m, tau, work, -1, 0)
+    results = lapack_routine(m, n, a, max(1, m), tau, work, -1, 0)
     if results['info'] != 0:
         raise LinAlgError('%s returns %d' % (routine_name, results['info']))
 
     # do qr decomposition
-    lwork = int(abs(work[0]))
+    lwork = max(1, n, int(abs(work[0])))
     work = zeros((lwork,), t)
-    results = lapack_routine(m, n, a, m, tau, work, lwork, 0)
+    results = lapack_routine(m, n, a, max(1, m), tau, work, lwork, 0)
     if results['info'] != 0:
         raise LinAlgError('%s returns %d' % (routine_name, results['info']))
 
@@ -918,14 +918,14 @@ def qr(a, mode='reduced'):
     # determine optimal lwork
     lwork = 1
     work = zeros((lwork,), t)
-    results = lapack_routine(m, mc, mn, q, m, tau, work, -1, 0)
+    results = lapack_routine(m, mc, mn, q, max(1, m), tau, work, -1, 0)
     if results['info'] != 0:
         raise LinAlgError('%s returns %d' % (routine_name, results['info']))
 
     # compute q
-    lwork = int(abs(work[0]))
+    lwork = max(1, n, int(abs(work[0])))
     work = zeros((lwork,), t)
-    results = lapack_routine(m, mc, mn, q, m, tau, work, lwork, 0)
+    results = lapack_routine(m, mc, mn, q, max(1, m), tau, work, lwork, 0)
     if results['info'] != 0:
         raise LinAlgError('%s returns %d' % (routine_name, results['info']))
 

diff --git a/numpy/linalg/tests/test_linalg.py b/numpy/linalg/tests/test_linalg.py
@@ -1582,9 +1582,25 @@ def check_qr(self, a):
         assert_(isinstance(r2, a_type))
         assert_almost_equal(r2, r1)
 
-    def test_qr_empty(self):
-        a = np.zeros((0, 2))
-        assert_raises(linalg.LinAlgError, linalg.qr, a)
+
+    @pytest.mark.parametrize(["m", "n"], [
+        (3, 0),
+        (0, 3),
+        (0, 0)
+    ])
+    def test_qr_empty(self, m, n):
+        k = min(m, n)
+        a = np.empty((m, n))
+        a_type = type(a)
+        a_dtype = a.dtype
+
+        self.check_qr(a)
+
+        h, tau = np.linalg.qr(a, mode='raw')
+        assert_equal(h.dtype, np.double)
+        assert_equal(tau.dtype, np.double)
+        assert_equal(h.shape, (n, m))
+        assert_equal(tau.shape, (k,))
 
     def test_mode_raw(self):
         # The factorization is not unique and varies between libraries,
@@ -1625,15 +1641,6 @@ def test_mode_all_but_economic(self):
             self.check_qr(m2)
             self.check_qr(m2.T)
 
-    def test_0_size(self):
-        # There may be good ways to do (some of this) reasonably:
-        a = np.zeros((0, 0))
-        assert_raises(linalg.LinAlgError, linalg.qr, a)
-        a = np.zeros((0, 1))
-        assert_raises(linalg.LinAlgError, linalg.qr, a)
-        a = np.zeros((1, 0))
-        assert_raises(linalg.LinAlgError, linalg.qr, a)
-
 
 class TestCholesky(object):
     # TODO: are there no other tests for cholesky?