minimal set of changes for returning failure to find non-zero pivot in FFGJ

Author: bjodah

symengine/lib/symengine.pxd

@@ -687,7 +687,7 @@ cdef extern from "<symengine/matrix.h>" namespace "SymEngine":
         DenseMatrix &B) except+ nogil
     void FFLU_solve "SymEngine::fraction_free_LU_solve"(const DenseMatrix &A,
         const DenseMatrix &b, DenseMatrix &x) except+ nogil
-    void FFGJ_solve "SymEngine::fraction_free_gauss_jordan_solve"(const DenseMatrix &A,
+    int FFGJ_solve "SymEngine::fraction_free_gauss_jordan_solve"(const DenseMatrix &A,
         const DenseMatrix &b, DenseMatrix &x) except+ nogil
     void LDL_solve "SymEngine::LDL_solve"(const DenseMatrix &A, const DenseMatrix &b,
         DenseMatrix &x) except+ nogil

symengine/lib/symengine_wrapper.in.pyx

@@ -3998,9 +3998,11 @@ cdef class DenseMatrixBase(MatrixBase):
                 deref(symengine.static_cast_DenseMatrix(b_.thisptr)),
                 deref(symengine.static_cast_DenseMatrix(x.thisptr)))
         elif method.upper() == 'FFGJ':
-            symengine.FFGJ_solve(deref(symengine.static_cast_DenseMatrix(self.thisptr)),
+            failure = symengine.FFGJ_solve(deref(symengine.static_cast_DenseMatrix(self.thisptr)),
                 deref(symengine.static_cast_DenseMatrix(b_.thisptr)),
                 deref(symengine.static_cast_DenseMatrix(x.thisptr)))
+            if (failure != 0):
+                raise Exception("Underdetermined system. Failed to find non-zero pivot in column: %d" % failure)
         else:
             raise Exception("Unsupported method.")
 

symengine/tests/test_matrices.py

@@ -11,7 +11,7 @@
     have_numpy = True
 except ImportError:
     have_numpy = False
-    
+
 try:
     import sympy
     from sympy.core.cache import clear_cache
@@ -444,6 +444,15 @@ def test_solve():
     x = A.solve(b, 'FFGJ')
     assert x == y
 
+    B = DenseMatrix(2, 2, [0]*4)
+    try:
+        B.solve(b, 'FFGJ')
+    except Exception:
+        pass
+    else:
+        raise Exception("this operation should have raised an exception")
+
+
 
 def test_FFLU():
     A = DenseMatrix(4, 4, [1, 2, 3, 4, 2, 2, 3, 4, 3, 3, 3, 4, 9, 8, 7, 6])