diff --git a/opencl_fdfd/csr.py b/opencl_fdfd/csr.py
index e42ad8f..e24e780 100644
--- a/opencl_fdfd/csr.py
+++ b/opencl_fdfd/csr.py
@@ -5,6 +5,7 @@ import pyopencl.array
 
 import time
 
+import fdfd_tools.operators
 
 from . import ops
 
@@ -106,6 +107,28 @@ def cg(a, b, max_iters=10000, err_thresh=1e-6, context=None, queue=None, verbose
     print('final error', errs[-1])
     print('overhead {} sec'.format(start_time2 - start_time))
 
-    print('Post-everything residual:', norm(a @ x - b) / norm(b))
+    print('Final residual:', norm(a @ x - b) / norm(b))
     return x
 
+
+def cg_solver(omega, dxes, J, epsilon, mu=None, pec=None, pmc=None, adjoint=False, solver_opts=None):
+    b0 = -1j * omega * J
+    A0 = fdfd_tools.operators.e_full(omega, dxes, epsilon=epsilon, mu=mu, pec=pec, pmc=pmc)
+
+    Pl, Pr = fdfd_tools.operators.e_full_preconditioners(dxes)
+
+    if adjoint:
+        A = (Pl @ A0 @ Pr).H
+        b = Pr.H @ b0
+    else:
+        A = Pl @ A0 @ Pr
+        b = Pl @ b0
+
+    x = cg(A.tocsr(), b, **solver_opts)
+
+    if adjoint:
+        x0 = Pl.H @ x
+    else:
+        x0 = Pr @ x
+
+    return x0