init differentiation

numethods/__init__.py

@@ -6,6 +6,14 @@ from .orthogonal import (
     QRSolver,
     LeastSquaresSolver,
 )
+from .differentiation import (
+    ForwardDiff,
+    BackwardDiff,
+    CentralDiff,
+    CentralDiff4th,
+    SecondDerivative,
+    RichardsonExtrap,
+)
 from .solvers import LUDecomposition, GaussJordan, Jacobi, GaussSeidel, Cholesky
 from .roots import Bisection, FixedPoint, Secant, NewtonRoot
 from .interpolation import NewtonInterpolation, LagrangeInterpolation