From 8fdc4460b9065f8a6cd7e95e106bfeafdc64d613 Mon Sep 17 00:00:00 2001
From: Jeremy Chen <convexset@gmail.com>
Date: Wed, 1 Aug 2018 01:00:07 +0800
Subject: ENH: handle empty matrices in qr decomposition (#11593)

Ensure LWORK and LDA respect the requirements of the lapack methods (zgeqrf, dgeqrf, zungqr, dorgqr)
---
 numpy/linalg/linalg.py | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

(limited to 'numpy/linalg/linalg.py')

diff --git a/numpy/linalg/linalg.py b/numpy/linalg/linalg.py
index f3a3b37a3..c3b76ada7 100644
--- 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']))
 
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