Use Expr.equals to do zero-equivalence test in Matrix.rref

Fix is similar to sympy/sympy#10650, thanks to @rpisarev.  In case of
zero-decision problem - we raise NotImplementedError.

Closes diofant#288
Closes sympy/sympy#9480

(Maybe it fixes also sympy/sympy#11238)

See sympy/sympy#10280 for alternative.

Author: skirpichev

sympy/matrices/matrices.py

@@ -24,7 +24,10 @@
 
 def _iszero(x):
     """Returns True if x is zero."""
-    return x.is_zero
+    r = x.equals(0)
+    if r is None:
+        raise NotImplementedError("Zero-decision problem for %s" % x)
+    return r
 
 
 class MatrixError(Exception):

sympy/matrices/tests/test_matrices.py

@@ -2495,3 +2495,31 @@ def test_issue_9422():
     assert x*M1 != M1*x
     assert a*M1 == M1*a
     assert y*x*M == Matrix([[y*x, 0], [0, y*x]])
+
+
+def test_issue_9480():
+    m = Matrix([[-5 + 5*sqrt(2), -5],
+                [-5*sqrt(2)/2 + 5, -5*sqrt(2)/2]])
+    assert m.rank() == 1
+
+
+def test_diofantissue_288():
+    k = Symbol('k')
+    m = Matrix([[-exp(I*k)*I/(4*k) + S.Half + exp(-I*k)*I/(4*k),
+                 exp(I*k)*I/(4*k) + S.Half - exp(-I*k)*I/(4*k),
+                 exp(I*k)/4 + S.Half + exp(-I*k)/4,
+                 -exp(I*k)/4 - S.Half - exp(-I*k)/4],
+                [exp(I*k)*I/(4*k) + S.Half - exp(-I*k)*I/(4*k),
+                 -exp(I*k)*I/(4*k) + S.Half + exp(-I*k)*I/(4*k),
+                 -exp(I*k)/4 - S.Half - exp(-I*k)/4,
+                 exp(I*k)/4 + S.Half + exp(-I*k)/4],
+                [exp(I*k)/4 + S.Half + exp(-I*k)/4,
+                 -exp(I*k)/4 - S.Half - exp(-I*k)/4,
+                 exp(I*k)*I*k/4 - exp(-I*k)*I*k/4,
+                 -exp(I*k)*I*k/4 + exp(-I*k)*I*k/4],
+                [-exp(I*k)/4 - 1/2 - exp(-I*k)/4,
+                 exp(I*k)/4 + 1/2 + exp(-I*k)/4,
+                 -exp(I*k)*I*k/4 + exp(-I*k)*I*k/4,
+                 exp(I*k)*I*k/4 - exp(-I*k)*I*k/4]])
+    assert m.det() == 0
+    assert m.rank() != 4