Ignore imaginary terms of problem matrix

If the imaginary part of all matrix elemts is zero, the matrix is tranformed into a real matrix. If there are imaginary terms != 0, a warning is lgged.

src/modules/solvers/QAOA.py

@@ -151,7 +151,12 @@ def run(self, mapped_problem: any, device_wrapper: any, config: Config, **kwargs
         """
 
         j = mapped_problem['J']
-
+        if np.any(np.iscomplex(j)):
+            logging.warning("The problem matrix of the QAOA solver contains imaginary numbers."
+                            "This may lead to an error later in the run.")
+        else:
+            j = np.real(j)
+
         # set up the problem
         n_qubits = j.shape[0]