diff --git a/src/discovery/likelihood.py b/src/discovery/likelihood.py
index faba0bc..9fd2e66 100644
--- a/src/discovery/likelihood.py
+++ b/src/discovery/likelihood.py
@@ -492,11 +492,12 @@ def cond(params):
 
 
 class ArrayLikelihood:
-    def __init__(self, psls, *, commongp=None, globalgp=None, transform=None):
+    def __init__(self, psls, *, commongp=None, globalgp=None, transform=None, decenter=False):
         self.psls = psls
         self.commongp = commongp
         self.globalgp = globalgp
         self.transform = transform
+        self.decenter = decenter
 
     # @functools.cached_property
     # def cloglast(self):
@@ -531,16 +532,59 @@ def loglike(params):
         else:
             # merge common GPs and global GP
             cgp = self.commongp if isinstance(self.commongp, list) else [self.commongp]
+            gplist = cgp + [self.globalgp]
             commongp = matrix.VectorCompoundGP(cgp + [self.globalgp])
 
         Ns, self.ys = zip(*[(psl.N, psl.y) for psl in self.psls])
+
+        # Both this line, and the decentering code below assumes that
+        # N and F are constants.
         self.vsm = matrix.VectorWoodburyKernel_varP(Ns, commongp.F, commongp.Phi)
+
+        if self.decenter:
+            # create decentering transformation
+
+            NmFs, ldNs = zip(*[N.solve_2d(F) for N, F in zip(self.vsm.Ns, self.vsm.Fs)])
+            FtNmFs = [F.T @ NmF for F, NmF in zip(self.vsm.Fs, NmFs)]
+            NmFtys = [NmF.T @ y for NmF, y in zip(NmFs, self.ys)]
+            FtNmF, NmFty = matrix.jnparray(FtNmFs), matrix.jnparray(NmFtys)
+            def decenter_transform(params, c):
+                phis_invs_commongp = [gp.Phi.getN(params)**-1 for gp in (self.commongp if isinstance(self.commongp, list) else [self.commongp])]
+                # get diagonal piece of the globalGP (decenter using CURN)
+                if self.globalgp is not None:
+                    phis_invs_globalgp = matrix.jnp.diag(self.globalgp.Phi.getN(params)**-1).reshape((len(self.psls), -1))
+                    phis_invs = matrix.jnp.concatenate([*phis_invs_commongp, phis_invs_globalgp], axis=1)
+                else:
+                    phis_invs = matrix.jnp.concatenate([*phis_invs_commongp], axis=1)
+                i1, i2 = matrix.jnp.diag_indices(phis_invs.shape[1], ndim=2)
+
+                # supposedly, the native batching here should be better
+                # than vmap.
+
+                cf = matrix.matrix_factor(FtNmF.at[:,i1,i2].add(phis_invs), lower=True)
+                am = matrix.jsp.linalg.solve_triangular(cf[0], c, trans=1, lower=cf[1])
+                mus = matrix.matrix_solve(cf, NmFty)
+                # jacobian of our transformation | d f^{-1} / d(xi) | = |L|. cf[0] is L^{-1}.
+                ldL = -matrix.jnp.logdet(cf[0][:,i1,i2])
+
+                c = am + mus
+
+                return c, ldL
+            decenter_transform.params = []
+
+
         if hasattr(commongp, 'prior'):
             self.vsm.prior = commongp.prior
         if hasattr(commongp, 'index'):
             self.vsm.index = commongp.index
 
-        loglike = self.vsm.make_kernelproduct_gpcomponent(self.ys, transform=self.transform)
+        if self.transform is not None and self.decenter is True:
+            raise ValueError("Can't decenter and add a transformation right now.")
+
+        if self.decenter:
+            loglike = self.vsm.make_kernelproduct_gpcomponent(self.ys, transform=decenter_transform)
+        else:
+            loglike = self.vsm.make_kernelproduct_gpcomponent(self.ys, transform=self.transform)
 
         return loglike
 
diff --git a/src/discovery/matrix.py b/src/discovery/matrix.py
index b6b0e38..9f2e1fe 100644
--- a/src/discovery/matrix.py
+++ b/src/discovery/matrix.py
@@ -1312,6 +1312,33 @@ def kernelsolve(params):
 
         return kernelsolve
 
+    def make_kernelsolve_simple(self, y):
+        # for when there is only one
+        # GP, and it hasn't been marginalized over
+        P_var = self.P_var
+        Nvar = self.N
+        F = jnparray(self.F)
+        y = jnparray(y)
+        P_var_inv = P_var.make_inv()
+        NmF, ldN = self.N.solve_2d(self.F)
+        FtNm = NmF.T
+        FtNmy = FtNm @ y
+        FtNmF = F.T @ NmF
+
+        Nvar_solve_2d = Nvar.make_solve_2d()
+        def kernelsolve(params):
+            Pinv, ldP = P_var_inv(params)
+            Sigma = Pinv + FtNmF
+            ch = matrix_factor(Sigma)
+            b_mean = matrix_solve(ch, FtNmy)
+
+            return b_mean, Sigma
+
+        kernelsolve.params = sorted(self.N.params + P_var.params)
+        return kernelsolve
+
+
+
     def make_kernelproduct_vary(self, y):
         NmF, ldN = self.N.solve_2d(self.F)
         FtNmF = self.F.T @ NmF
@@ -1869,6 +1896,8 @@ def make_kernelproduct_gpcomponent(self, ys, transform=None):
         FtNmF, NmFty = jnparray(FtNmFs), jnparray(NmFtys)
         ytNmy, ldN = float(sum(ytNmys)), float(sum(ldNs))
 
+        n_psr = len(FtNmFs)
+
         if isinstance(self.index, list):
             cvarsall = self.index
         else:
@@ -1890,18 +1919,23 @@ def unfold(c):
 
             def kernelproduct(params):
                 c = fold(params)
-
+                ldL = 0.0
                 if transform is not None:
-                    c, ldL = transform(params, c)
+                    c, tmp_ldL = transform(params, c)
+                    ldL += tmp_ldL
                     params = {**params, **unfold(c)}
                 else:
-                    ldL = 0.0
+                    ldL += 0.0
+
 
                 logpr = P_var_prior(params)
 
                 ret = (-0.5 * ytNmy + jnp.sum(c * NmFty) - 0.5 * jnp.einsum('ij,ijk,ik', c, FtNmF, c)
-                       -0.5 * ldN - logpr + ldL)
-                return (ret, c) if transform is not None else ret
+                       -0.5 * ldN + logpr + ldL)
+                if transform:
+                    return (ret, c)
+                else:
+                    return ret
 
             kernelproduct.params = sorted(set(P_var_prior.params +
                                               sum([list(cvars) for cvars in cvarsall], []) +
diff --git a/src/discovery/signals.py b/src/discovery/signals.py
index dfd4933..54b5076 100644
--- a/src/discovery/signals.py
+++ b/src/discovery/signals.py
@@ -546,7 +546,14 @@ def priorfunc(params):
 
             # the jnp.dot handles the "pixel basis" case where the elements of orfmat are n-vectors
             # and phidiag is an (m x n)-matrix; here n is the number of pixels and m of Fourier components
-            return jnp.block([[jnp.make2d(jnp.dot(phi, val)) for val in row] for row in orfmat])
+            #
+            if jnp is jax.numpy:
+                # this seems to speed things up, pre-compilation at least.
+                tmp = jnp.kron(orfmat, jnp.diag(phi))
+                return tmp
+            else:
+                return jnp.block([[jnp.make2d(jnp.dot(phi, val)) for val in row] for row in orfmat])
+
         priorfunc.params = argmap
         priorfunc.type = jax.Array
 
@@ -562,8 +569,10 @@ def invprior(params):
                 # log |S_ij Gamma_ab| = log (prod_i S_i^npsr) + log prod_i |Gamma_ab|
                 #                     = npsr * sum_i log S_i + nfreqs |Gamma_ab|
 
-                return (jnp.block([[jnp.make2d(val * invphi) for val in row] for row in invorf]),
-                        phi.shape[0] * orflogdet + orfmat.shape[0] * logdetphi)
+                # return (jnp.block([[jnp.make2d(val * invphi) for val in row] for row in invorf]),
+                #         phi.shape[0] * orflogdet + orfmat.shape[0] * logdetphi)
+                return (jnp.kron(invorf, jnp.make2d(invphi)),
+                            phi.shape[0] * orflogdet + orfmat.shape[0] * logdetphi)
                         # was -orfmat.shape[0] * jnp.sum(jnp.log(invphidiag)))
             invprior.params = argmap
             invprior.type = jax.Array