Use free_symbols from C++

Author: isuruf

symengine/lib/symengine.pxd

@@ -893,6 +893,7 @@ cdef extern from "<symengine/visitor.h>" namespace "SymEngine":
     bool has_symbol(const Basic &b, const Symbol &x) nogil except +
     rcp_const_basic coeff(const Basic &b, const Basic &x, const Basic &n) nogil except +
     set_basic free_symbols(const Basic &b) nogil except +
+    set_basic free_symbols(const MatrixBase &b) nogil except +
     unsigned count_ops(const vec_basic &a) nogil
 
 cdef extern from "<symengine/logic.h>" namespace "SymEngine":

symengine/lib/symengine_wrapper.pyx

@@ -3488,11 +3488,8 @@ cdef class DenseMatrixBase(MatrixBase):
 
     @property
     def free_symbols(self):
-        s = set()
-        for i in range(self.nrows()):
-            for j in range(self.ncols()):
-                s.update(self._get(i, j).free_symbols)
-        return s
+        cdef symengine.set_basic _set = symengine.free_symbols(deref(self.thisptr))
+        return {c2py(<rcp_const_basic>(elem)) for elem in _set}
 
     def _submatrix(self, unsigned r_i, unsigned c_i, unsigned r_j, unsigned c_j, unsigned r_s=1, unsigned c_s=1):
         r_j, c_j = r_j - 1, c_j - 1