Increase the usage of augmented assignment statements

[elfring]

👀 Some source code analysis tools can help to find opportunities for improving software components.
💭 I propose to increase the usage of augmented assignment statements accordingly.

diff --git a/PythonLinearNonlinearControl/controllers/mpc.py b/PythonLinearNonlinearControl/controllers/mpc.py
index c1e0db3..7f8c001 100644
--- a/PythonLinearNonlinearControl/controllers/mpc.py
+++ b/PythonLinearNonlinearControl/controllers/mpc.py
@@ -167,7 +167,7 @@ class LinearMPC(Controller):
 
 H = np.matmul(self.theta_mat.T, np.matmul(self.Qs, self.theta_mat)) \
 + self.Rs
- H = H * 0.5
+ H *= 0.5
 
 # constraints
 A = []
diff --git a/PythonLinearNonlinearControl/controllers/nmpc_cgmres.py b/PythonLinearNonlinearControl/controllers/nmpc_cgmres.py
index 70e722b..74432af 100644
--- a/PythonLinearNonlinearControl/controllers/nmpc_cgmres.py
+++ b/PythonLinearNonlinearControl/controllers/nmpc_cgmres.py
@@ -126,7 +126,7 @@ class NMPCCGMRES(Controller):
 
 for j in range(i + 1):
 hs[j, i] = np.dot(Av, vs[:, j])
- sum_Av = sum_Av + hs[j, i] * vs[:, j]
+ sum_Av += hs[j, i] * vs[:, j]
 
 v_est = Av - sum_Av