Beispiel #1
0
    def test_predict_dipolar(self):

        h = [0.05, 0.05]
        meshObj = Mesh.TensorMesh((h, h, h), x0='CCC')

        dchi = 0.01
        tau1 = 1e-8
        tau2 = 1e0
        mod = (dchi / np.log(tau2 / tau1)) * np.ones(meshObj.nC)

        times = np.logspace(-4, -2, 3)
        waveObj = VRM.WaveformVRM.SquarePulse(delt=0.02)

        phi = np.random.uniform(-np.pi, np.pi)
        psi = np.random.uniform(-np.pi, np.pi)
        R = 2.
        loc_rx = R * np.c_[np.sin(phi) * np.cos(psi),
                           np.sin(phi) * np.sin(psi),
                           np.cos(phi)]

        rxList = [
            VRM.Rx.Point(loc_rx, times=times, fieldType='dhdt', fieldComp='x')
        ]
        rxList.append(
            VRM.Rx.Point(loc_rx, times=times, fieldType='dhdt', fieldComp='y'))
        rxList.append(
            VRM.Rx.Point(loc_rx, times=times, fieldType='dhdt', fieldComp='z'))

        alpha = np.random.uniform(0, np.pi)
        beta = np.random.uniform(-np.pi, np.pi)
        loc_tx = [0., 0., 0.]
        Src = VRM.Src.CircLoop(rxList, loc_tx, 25., np.r_[alpha, beta], 1.,
                               waveObj)
        txList = [Src]

        Survey = VRM.Survey(txList)
        Problem = VRM.Problem_Linear(meshObj, ref_factor=0)
        Problem.pair(Survey)
        Fields = Problem.fields(mod)

        H0 = Src.getH0(np.c_[0., 0., 0.])
        dmdtx = -H0[0, 0] * 0.1**3 * (dchi / np.log(tau2 / tau1)) * (
            1 / times[1] - 1 / (times[1] + 0.02))
        dmdty = -H0[0, 1] * 0.1**3 * (dchi / np.log(tau2 / tau1)) * (
            1 / times[1] - 1 / (times[1] + 0.02))
        dmdtz = -H0[0, 2] * 0.1**3 * (dchi / np.log(tau2 / tau1)) * (
            1 / times[1] - 1 / (times[1] + 0.02))
        dmdot = np.dot(np.r_[dmdtx, dmdty, dmdtz], loc_rx.T)

        fx = (1 /
              (4 * np.pi)) * (3 * loc_rx[0, 0] * dmdot / R**5 - dmdtx / R**3)
        fy = (1 /
              (4 * np.pi)) * (3 * loc_rx[0, 1] * dmdot / R**5 - dmdty / R**3)
        fz = (1 /
              (4 * np.pi)) * (3 * loc_rx[0, 2] * dmdot / R**5 - dmdtz / R**3)

        self.assertTrue(
            np.all(
                np.abs(Fields[1:-1:3] - np.r_[fx, fy, fz]) < 1e-5 *
                np.sqrt((Fields[1:-1:3]**2).sum())))
Beispiel #2
0
    def test_basic_inversion(self):
        """
        Test to see if inversion recovers model
        """

        h = [(2, 30)]
        meshObj = Mesh.TensorMesh((h, h, [(2, 10)]), x0='CCN')

        mod = 0.00025 * np.ones(meshObj.nC)
        mod[(meshObj.gridCC[:, 0] > -4.) & (meshObj.gridCC[:, 1] > -4.) &
            (meshObj.gridCC[:, 0] < 4.) & (meshObj.gridCC[:, 1] < 4.)] = 0.001

        times = np.logspace(-4, -2, 5)
        waveObj = VRM.WaveformVRM.SquarePulse(0.02)

        x, y = np.meshgrid(np.linspace(-17, 17, 16), np.linspace(-17, 17, 16))
        x, y, z = mkvc(x), mkvc(y), 0.5 * np.ones(np.size(x))
        rxList = [VRM.Rx.Point(np.c_[x, y, z], times, 'dbdt', 'z')]

        txNodes = np.array([[-20, -20, 0.001], [20, -20,
                                                0.001], [20, 20, 0.001],
                            [-20, 20, 0.01], [-20, -20, 0.001]])
        txList = [VRM.Src.LineCurrent(rxList, txNodes, 1., waveObj)]

        Survey = VRM.Survey(txList)
        Problem = VRM.Problem_Linear(meshObj, refFact=2)
        Problem.pair(Survey)
        Survey.makeSyntheticData(mod)
        Survey.eps = 1e-11

        dmis = DataMisfit.l2_DataMisfit(Survey)
        W = mkvc((np.sum(np.array(Problem.A)**2, axis=0)))**0.25
        reg = Regularization.Simple(meshObj,
                                    alpha_s=0.01,
                                    alpha_x=1.,
                                    alpha_y=1.,
                                    alpha_z=1.,
                                    cell_weights=W)
        opt = Optimization.ProjectedGNCG(maxIter=20,
                                         lower=0.,
                                         upper=1e-2,
                                         maxIterLS=20,
                                         tolCG=1e-4)
        invProb = InvProblem.BaseInvProblem(dmis, reg, opt)
        directives = [
            Directives.BetaSchedule(coolingFactor=2, coolingRate=1),
            Directives.TargetMisfit()
        ]
        inv = Inversion.BaseInversion(invProb, directiveList=directives)

        m0 = 1e-6 * np.ones(len(mod))
        mrec = inv.run(m0)

        dmis_final = np.sum(
            (dmis.W.diagonal() * (Survey.dobs - Problem.fields(mrec)))**2)
        mod_err_2 = np.sqrt(np.sum((mrec - mod)**2)) / np.size(mod)
        mod_err_inf = np.max(np.abs(mrec - mod))

        self.assertTrue(dmis_final < Survey.nD and mod_err_2 < 5e-6
                        and mod_err_inf < np.max(mod))
Beispiel #3
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    def test_convergence_radial(self):
        """
        Test the convergence of the solution to analytic results from
        Cowan (2016) and test accuracy
        """

        h = [(2, 30)]
        meshObj = Mesh.TensorMesh((h, h, [(2, 20)]), x0='CCN')

        dchi = 0.01
        tau1 = 1e-8
        tau2 = 1e0
        mod = (dchi / np.log(tau2 / tau1)) * np.ones(meshObj.nC)

        times = np.array([1e-3])
        waveObj = VRM.WaveformVRM.SquarePulse(0.02)

        z = 0.25
        a = 5
        # rxList = [VRM.Rx.Point_dhdt(np.c_[a, 0., z], times, 'x')]
        # rxList.append(VRM.Rx.Point_dhdt(np.c_[0., a, z], times, 'y'))
        rxList = [VRM.Rx.Point(np.c_[a, 0., z], times, 'dhdt', 'x')]
        rxList.append(VRM.Rx.Point(np.c_[0., a, z], times, 'dhdt', 'y'))
        txList = [
            VRM.Src.CircLoop(rxList, np.r_[0., 0., z], a, np.r_[0., 0.], 1.,
                             waveObj)
        ]

        Survey2 = VRM.Survey(txList)
        Survey3 = VRM.Survey(txList)
        Survey4 = VRM.Survey(txList)
        Survey5 = VRM.Survey(txList)
        Problem2 = VRM.Problem_Linear(meshObj, refFact=2)
        Problem3 = VRM.Problem_Linear(meshObj, refFact=3)
        Problem4 = VRM.Problem_Linear(meshObj, refFact=4)
        Problem5 = VRM.Problem_Linear(meshObj, refFact=5)
        Problem2.pair(Survey2)
        Problem3.pair(Survey3)
        Problem4.pair(Survey4)
        Problem5.pair(Survey5)
        Fields2 = Problem2.fields(mod)
        Fields3 = Problem3.fields(mod)
        Fields4 = Problem4.fields(mod)
        Fields5 = Problem5.fields(mod)

        gamma = 4 * z * (2 / np.pi)**1.5
        F = -(1 / np.log(tau2 / tau1)) * (1 / times - 1 / (times + 0.02))
        Fields_true = 0.5 * (dchi / (2 + dchi)) * (np.pi * gamma)**-1 * F

        ErrsX = np.abs((np.r_[Fields2[0], Fields3[0], Fields4[0], Fields5[0]] -
                        Fields_true) / Fields_true)
        ErrsY = np.abs((np.r_[Fields2[1], Fields3[1], Fields4[1], Fields5[1]] -
                        Fields_true) / Fields_true)

        Testx1 = ErrsX[-1] < 0.01
        Testy1 = ErrsY[-1] < 0.01
        Testx2 = np.all(ErrsX[1:] - ErrsX[0:-1] < 0.)
        Testy2 = np.all(ErrsY[1:] - ErrsY[0:-1] < 0.)

        self.assertTrue(Testx1 and Testx2 and Testy1 and Testy2)
Beispiel #4
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    def test_convergence_vertical(self):
        """
        Test the convergence of the solution to analytic results from
        Cowan (2016) and test accuracy
        """

        h = [(2, 20)]
        meshObj = Mesh.TensorMesh((h, h, h), x0='CCN')

        dchi = 0.01
        tau1 = 1e-8
        tau2 = 1e0
        mod = (dchi / np.log(tau2 / tau1)) * np.ones(meshObj.nC)

        times = np.array([1e-3])
        waveObj = VRM.WaveformVRM.SquarePulse(delt=0.02)

        z = 0.5
        a = 0.1
        loc_rx = np.c_[0., 0., z]
        rxList = [
            VRM.Rx.Point(loc_rx, times=times, fieldType='dhdt', fieldComp='z')
        ]
        txList = [
            VRM.Src.CircLoop(rxList, np.r_[0., 0., z], a, np.r_[0., 0.], 1.,
                             waveObj)
        ]

        Survey2 = VRM.Survey(txList)
        Survey3 = VRM.Survey(txList)
        Survey4 = VRM.Survey(txList)
        Survey5 = VRM.Survey(txList)
        Problem2 = VRM.Problem_Linear(meshObj, ref_factor=2)
        Problem3 = VRM.Problem_Linear(meshObj, ref_factor=3)
        Problem4 = VRM.Problem_Linear(meshObj, ref_factor=4)
        Problem5 = VRM.Problem_Linear(meshObj, ref_factor=5)
        Problem2.pair(Survey2)
        Problem3.pair(Survey3)
        Problem4.pair(Survey4)
        Problem5.pair(Survey5)
        Fields2 = Problem2.fields(mod)
        Fields3 = Problem3.fields(mod)
        Fields4 = Problem4.fields(mod)
        Fields5 = Problem5.fields(mod)

        F = -(1 / np.log(tau2 / tau1)) * (1 / times - 1 / (times + 0.02))
        Fields_true = (0.5 * np.pi * a**2 / np.pi) * (dchi / (2 + dchi)) * (
            (2 * z)**2 + a**2)**-1.5 * F

        Errs = np.abs(
            (np.r_[Fields2, Fields3, Fields4, Fields5] - Fields_true) /
            Fields_true)

        Test1 = Errs[-1] < 0.005
        Test2 = np.all(Errs[1:] - Errs[0:-1] < 0.)

        self.assertTrue(Test1 and Test2)
Beispiel #5
0
loc = np.c_[mkvc(x), mkvc(y), mkvc(z)]  # Src and Rx Locations

srcListVRM = []

for pp in range(0, loc.shape[0]):

    loc_pp = np.reshape(loc[pp, :], (1, 3))
    rxListVRM = [
        VRM.Rx.Point(loc_pp, times=times, fieldType='dbdt', fieldComp='z')
    ]

    srcListVRM.append(
        VRM.Src.MagDipole(rxListVRM, mkvc(loc[pp, :]), [0., 0., 0.01],
                          waveform))

survey_vrm = VRM.Survey(srcListVRM)

##########################################################################
# Forward Problem
# ---------------
#
# Here we predict data by solving the forward problem. For the VRM problem,
# we use a sensitivity refinement strategy for cells # that are proximal to
# transmitters. This is controlled through the *ref_factor* and *ref_radius*
# properties.
#

# Defining the forward problem
problem_vrm = VRM.Problem_Linear(mesh,
                                 indActive=topoCells,
                                 ref_factor=3,
Beispiel #6
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    def test_sources(self):
        """
        Multiple source classes are used to make a small dipole source with the
        same orientation and dipole moment. Test ensures the same fields are
        computed.
        """

        h = [0.5, 0.5]
        meshObj = Mesh.TensorMesh((h, h, h), x0='CCC')

        dchi = 0.01
        tau1 = 1e-8
        tau2 = 1e0
        mod = (dchi / np.log(tau2 / tau1)) * np.ones(meshObj.nC)

        times = np.logspace(-4, -2, 3)
        waveObj = VRM.WaveformVRM.SquarePulse(delt=0.02)

        phi = np.random.uniform(-np.pi, np.pi)
        psi = np.random.uniform(-np.pi, np.pi)
        Rrx = 3.
        loc_rx = Rrx * np.c_[np.sin(phi) * np.cos(psi),
                             np.sin(phi) * np.sin(psi),
                             np.cos(phi)]

        rxList = [
            VRM.Rx.Point(loc_rx, times=times, fieldType='dhdt', fieldComp='x')
        ]
        rxList.append(
            VRM.Rx.Point(loc_rx, times=times, fieldType='dhdt', fieldComp='y'))
        rxList.append(
            VRM.Rx.Point(loc_rx, times=times, fieldType='dhdt', fieldComp='z'))

        alpha = np.random.uniform(0, np.pi)
        beta = np.random.uniform(-np.pi, np.pi)
        Rtx = 4.
        loc_tx = Rtx * np.r_[np.sin(alpha) * np.cos(beta),
                             np.sin(alpha) * np.sin(beta),
                             np.cos(alpha)]

        txList = [VRM.Src.MagDipole(rxList, loc_tx, [0., 0., 0.01], waveObj)]
        txList.append(
            VRM.Src.CircLoop(rxList, loc_tx, np.sqrt(0.01 / np.pi),
                             np.r_[0., 0.], 1., waveObj))
        px = loc_tx[0] + np.r_[-0.05, 0.05, 0.05, -0.05, -0.05]
        py = loc_tx[1] + np.r_[-0.05, -0.05, 0.05, 0.05, -0.05]
        pz = loc_tx[2] * np.ones(5)
        txList.append(
            VRM.Src.LineCurrent(rxList, np.c_[px, py, pz], 1., waveObj))

        Survey = VRM.Survey(txList)
        Problem = VRM.Problem_Linear(meshObj, ref_factor=1)
        Problem.pair(Survey)
        Fields = Problem.fields(mod)

        err1 = np.all(
            np.abs(Fields[9:18] - Fields[0:9]) /
            (np.abs(Fields[0:9]) + 1e-14) < 0.005)
        err2 = np.all(
            np.abs(Fields[18:] - Fields[0:9]) /
            (np.abs(Fields[0:9]) + 1e-14) < 0.005)
        err3 = np.all(
            np.abs(Fields[9:18] - Fields[18:]) /
            (np.abs(Fields[18:]) + 1e-14) < 0.005)

        self.assertTrue(err1 and err2 and err3)
Beispiel #7
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    def test_receiver_types(self):
        """
        Test ensures the fields predicted for each receiver type
        are correct.
        """

        h1 = [0.25, 0.25]
        meshObj_Tensor = Mesh.TensorMesh((h1, h1, h1), x0='CCN')

        chi0 = 0.
        dchi = 0.01
        tau1 = 1e-8
        tau2 = 1e0

        # Tensor Model
        mod = (dchi / np.log(tau2 / tau1)) * np.ones(meshObj_Tensor.nC)

        times = np.array([1e-3])
        waveObj = VRM.WaveformVRM.SquarePulse(delt=0.02)

        phi = np.random.uniform(-np.pi, np.pi)
        psi = np.random.uniform(-np.pi, np.pi)
        R = 5.
        loc_rx = R * np.c_[np.sin(phi) * np.cos(psi),
                           np.sin(phi) * np.sin(psi),
                           np.cos(phi)]
        loc_tx = 0.5 * np.r_[np.sin(phi) * np.cos(psi),
                             np.sin(phi) * np.sin(psi),
                             np.cos(phi)]

        rxList1 = [
            VRM.Rx.Point(loc_rx, times=times, fieldType='dhdt', fieldComp='x')
        ]
        rxList1.append(
            VRM.Rx.Point(loc_rx, times=times, fieldType='dhdt', fieldComp='y'))
        rxList1.append(
            VRM.Rx.Point(loc_rx, times=times, fieldType='dhdt', fieldComp='z'))

        w = 0.1
        N = 100
        rxList2 = [
            VRM.Rx.SquareLoop(loc_rx,
                              times=times,
                              width=w,
                              nTurns=N,
                              fieldType='dhdt',
                              fieldComp='x')
        ]
        rxList2.append(
            VRM.Rx.SquareLoop(loc_rx,
                              times=times,
                              width=w,
                              nTurns=N,
                              fieldType='dhdt',
                              fieldComp='y'))
        rxList2.append(
            VRM.Rx.SquareLoop(loc_rx,
                              times=times,
                              width=w,
                              nTurns=N,
                              fieldType='dhdt',
                              fieldComp='z'))

        txList1 = [VRM.Src.MagDipole(rxList1, loc_tx, [1., 1., 1.], waveObj)]
        txList2 = [VRM.Src.MagDipole(rxList2, loc_tx, [1., 1., 1.], waveObj)]

        Survey1 = VRM.Survey(txList1)
        Survey2 = VRM.Survey(txList2)
        Problem1 = VRM.Problem_Linear(meshObj_Tensor,
                                      ref_factor=2,
                                      ref_radius=[1.9, 3.6])
        Problem2 = VRM.Problem_Linear(meshObj_Tensor,
                                      ref_factor=2,
                                      ref_radius=[1.9, 3.6])
        Problem1.pair(Survey1)
        Problem2.pair(Survey2)
        Fields1 = Problem1.fields(mod)
        Fields2 = Problem2.fields(mod)

        Err = np.abs(Fields1 - Fields2)

        Test = np.all(Err < 1e-6)

        self.assertTrue(Test)
Beispiel #8
0
    def test_vs_mesh_vs_loguniform(self):
        """
        Test to make sure OcTree matches Tensor results and linear vs
        loguniform match
        """

        h1 = [(2, 4)]
        h2 = 0.5 * np.ones(16)
        meshObj_Tensor = Mesh.TensorMesh((h1, h1, h1), x0='000')
        meshObj_OcTree = Mesh.TreeMesh([h2, h2, h2], x0='000')

        x, y, z = np.meshgrid(np.c_[1., 3., 5., 7.], np.c_[1., 3., 5., 7.],
                              np.c_[1., 3., 5., 7.])
        x = x.reshape((4**3, 1))
        y = y.reshape((4**3, 1))
        z = z.reshape((4**3, 1))
        loc_rx = np.c_[x, y, z]
        meshObj_OcTree.insert_cells(loc_rx,
                                    2 * np.ones((4**3)),
                                    finalize=False)

        x, y, z = np.meshgrid(np.c_[1., 3., 5., 7.], np.c_[1., 3., 5., 7.],
                              np.c_[5., 7.])
        x = x.reshape((32, 1))
        y = y.reshape((32, 1))
        z = z.reshape((32, 1))
        loc_rx = np.c_[x, y, z]
        meshObj_OcTree.insert_cells(loc_rx, 3 * np.ones((32)), finalize=False)

        x, y, z = np.meshgrid(np.c_[3.5, 4.0, 4.5, 5.0, 5.5],
                              np.c_[3.5, 4.0, 4.5, 5.0, 5.5], np.c_[6.0, 6.5,
                                                                    7.0, 7.5])
        x = x.reshape((100, 1))
        y = y.reshape((100, 1))
        z = z.reshape((100, 1))
        loc_rx = np.c_[x, y, z]
        meshObj_OcTree.insert_cells(loc_rx, 4 * np.ones((100)), finalize=True)

        chi0 = 0.
        dchi = 0.01
        tau1 = 1e-8
        tau2 = 1e0

        # Tensor Models
        mod_a = (dchi / np.log(tau2 / tau1)) * np.ones(meshObj_Tensor.nC)
        mod_chi0_a = chi0 * np.ones(meshObj_Tensor.nC)
        mod_dchi_a = dchi * np.ones(meshObj_Tensor.nC)
        mod_tau1_a = tau1 * np.ones(meshObj_Tensor.nC)
        mod_tau2_a = tau2 * np.ones(meshObj_Tensor.nC)

        # OcTree Models
        mod_b = (dchi / np.log(tau2 / tau1)) * np.ones(meshObj_OcTree.nC)
        mod_chi0_b = chi0 * np.ones(meshObj_OcTree.nC)
        mod_dchi_b = dchi * np.ones(meshObj_OcTree.nC)
        mod_tau1_b = tau1 * np.ones(meshObj_OcTree.nC)
        mod_tau2_b = tau2 * np.ones(meshObj_OcTree.nC)

        times = np.array([1e-3])
        waveObj = VRM.WaveformVRM.SquarePulse(delt=0.02)

        loc_rx = np.c_[4., 4., 8.25]
        rxList = [
            VRM.Rx.Point(loc_rx, times=times, fieldType='dhdt', fieldComp='z')
        ]
        txList = [
            VRM.Src.MagDipole(rxList, np.r_[4., 4., 8.25], [0., 0., 1.],
                              waveObj)
        ]

        Survey1 = VRM.Survey(txList)
        Survey2 = VRM.Survey(txList)
        Survey3 = VRM.Survey(txList)
        Survey4 = VRM.Survey(txList)
        Problem1 = VRM.Problem_Linear(meshObj_Tensor,
                                      ref_factor=2,
                                      ref_radius=[1.9, 3.6])
        Problem2 = VRM.Problem_LogUniform(meshObj_Tensor,
                                          ref_factor=2,
                                          ref_radius=[1.9, 3.6],
                                          chi0=mod_chi0_a,
                                          dchi=mod_dchi_a,
                                          tau1=mod_tau1_a,
                                          tau2=mod_tau2_a)
        Problem3 = VRM.Problem_Linear(meshObj_OcTree, ref_factor=0)
        Problem4 = VRM.Problem_LogUniform(meshObj_OcTree,
                                          ref_factor=0,
                                          chi0=mod_chi0_b,
                                          dchi=mod_dchi_b,
                                          tau1=mod_tau1_b,
                                          tau2=mod_tau2_b)
        Problem1.pair(Survey1)
        Problem2.pair(Survey2)
        Problem3.pair(Survey3)
        Problem4.pair(Survey4)
        Fields1 = Problem1.fields(mod_a)
        Fields2 = Problem2.fields()
        Fields3 = Problem3.fields(mod_b)
        Fields4 = Problem4.fields()
        dpred1 = Survey1.dpred(mod_a)
        dpred2 = Survey2.dpred(mod_a)

        Err1 = np.abs((Fields1 - Fields2) / Fields1)
        Err2 = np.abs((Fields2 - Fields3) / Fields2)
        Err3 = np.abs((Fields3 - Fields4) / Fields3)
        Err4 = np.abs((Fields4 - Fields1) / Fields4)
        Err5 = np.abs((dpred1 - dpred2) / dpred1)

        Test1 = Err1 < 0.01
        Test2 = Err2 < 0.01
        Test3 = Err3 < 0.01
        Test4 = Err4 < 0.01
        Test5 = Err5 < 0.01

        self.assertTrue(Test1 and Test2 and Test3 and Test4 and Test5)
Beispiel #9
0
loc = np.c_[mkvc(x), mkvc(y), mkvc(z)]  # Src and Rx Locations

src_list_vrm = []

for pp in range(0, loc.shape[0]):

    loc_pp = np.reshape(loc[pp, :], (1, 3))
    rx_list_vrm = [
        VRM.Rx.Point(loc_pp, times=times, fieldType='dbdt', fieldComp='z')
    ]

    src_list_vrm.append(
        VRM.Src.MagDipole(rx_list_vrm, mkvc(loc[pp, :]), [0., 0., 0.01],
                          waveform))

survey_vrm = VRM.Survey(src_list_vrm)

##########################################################################
# Problem
# -------
#
# For the VRM problem, we used a sensitivity refinement strategy for cells
# that are proximal to transmitters. This is controlled through the
# *ref_factor* and *ref_radius* properties.
#

# Defining the problem
problem_vrm = VRM.Problem_Linear(mesh,
                                 indActive=topoCells,
                                 ref_factor=3,
                                 ref_radius=[1.25, 2.5, 3.75])
Beispiel #10
0
    def test_vs_mesh_vs_loguniform(self):
        """
        Test to make sure OcTree matches Tensor results and linear vs
        loguniform match
        """

        h1 = [(2, 4)]
        h2 = 0.5 * np.ones(16)
        meshObj_Tensor = Mesh.TensorMesh((h1, h1, h1), x0='000')
        meshObj_OcTree = Mesh.TreeMesh([h2, h2, h2], x0='000')

        meshObj_OcTree.refine(2)

        def refinefcn(cell):
            xyz = cell.center
            dist = ((xyz - [4., 4., 8.])**2).sum()**0.5
            if dist < 2.65:
                return 4
            return 2

        meshObj_OcTree.refine(refinefcn)

        chi0 = 0.
        dchi = 0.01
        tau1 = 1e-8
        tau2 = 1e0

        # Tensor Models
        mod_a = (dchi / np.log(tau2 / tau1)) * np.ones(meshObj_Tensor.nC)
        mod_chi0_a = chi0 * np.ones(meshObj_Tensor.nC)
        mod_dchi_a = dchi * np.ones(meshObj_Tensor.nC)
        mod_tau1_a = tau1 * np.ones(meshObj_Tensor.nC)
        mod_tau2_a = tau2 * np.ones(meshObj_Tensor.nC)

        # OcTree Models
        mod_b = (dchi / np.log(tau2 / tau1)) * np.ones(meshObj_OcTree.nC)
        mod_chi0_b = chi0 * np.ones(meshObj_OcTree.nC)
        mod_dchi_b = dchi * np.ones(meshObj_OcTree.nC)
        mod_tau1_b = tau1 * np.ones(meshObj_OcTree.nC)
        mod_tau2_b = tau2 * np.ones(meshObj_OcTree.nC)

        times = np.array([1e-3])
        waveObj = VRM.WaveformVRM.SquarePulse(0.02)

        loc_rx = np.c_[4., 4., 8.25]
        # rxList = [VRM.Rx.Point_dhdt(loc_rx, times, 'z')]
        rxList = [VRM.Rx.Point(loc_rx, times, 'dhdt', 'z')]
        txList = [
            VRM.Src.MagDipole(rxList, np.r_[4., 4., 8.25], [0., 0., 1.],
                              waveObj)
        ]

        Survey1 = VRM.Survey(txList)
        Survey2 = VRM.Survey(txList)
        Survey3 = VRM.Survey(txList)
        Survey4 = VRM.Survey(txList)
        Problem1 = VRM.Problem_Linear(meshObj_Tensor,
                                      refFact=2,
                                      refRadius=[1.9, 3.6])
        Problem2 = VRM.Problem_LogUniform(meshObj_Tensor,
                                          refFact=2,
                                          refRadius=[1.9, 3.6],
                                          chi0=mod_chi0_a,
                                          dchi=mod_dchi_a,
                                          tau1=mod_tau1_a,
                                          tau2=mod_tau2_a)
        Problem3 = VRM.Problem_Linear(meshObj_OcTree, refFact=0)
        Problem4 = VRM.Problem_LogUniform(meshObj_OcTree,
                                          refFact=0,
                                          chi0=mod_chi0_b,
                                          dchi=mod_dchi_b,
                                          tau1=mod_tau1_b,
                                          tau2=mod_tau2_b)
        Problem1.pair(Survey1)
        Problem2.pair(Survey2)
        Problem3.pair(Survey3)
        Problem4.pair(Survey4)
        Fields1 = Problem1.fields(mod_a)
        Fields2 = Problem2.fields()
        Fields3 = Problem3.fields(mod_b)
        Fields4 = Problem4.fields()
        dpred1 = Survey1.dpred(mod_a)
        dpred2 = Survey2.dpred(mod_a)

        Err1 = np.abs((Fields1 - Fields2) / Fields1)
        Err2 = np.abs((Fields2 - Fields3) / Fields2)
        Err3 = np.abs((Fields3 - Fields4) / Fields3)
        Err4 = np.abs((Fields4 - Fields1) / Fields4)
        Err5 = np.abs((dpred1 - dpred2) / dpred1)

        Test1 = Err1 < 0.001
        Test2 = Err2 < 0.001
        Test3 = Err3 < 0.001
        Test4 = Err4 < 0.001
        Test5 = Err5 < 0.001

        self.assertTrue(Test1 and Test2 and Test3 and Test4 and Test5)