from SimPEG import Mesh, Utils, np, SolverLU

def run(plotIt=True):

    """
        Mesh: Basic Forward 2D DC Resistivity
        =====================================

        2D DC forward modeling example with Tensor and Curvilinear Meshes
    """

    # Step1: Generate Tensor and Curvilinear Mesh
    sz = [40,40]
    tM = Mesh.TensorMesh(sz)
    rM = Mesh.CurvilinearMesh(Utils.meshutils.exampleLrmGrid(sz,'rotate'))

    # Step2: Direct Current (DC) operator
    def DCfun(mesh, pts):
        D = mesh.faceDiv
        sigma = 1e-2*np.ones(mesh.nC)
        MsigI = mesh.getFaceInnerProduct(sigma, invProp=True, invMat=True)
        A = -D*MsigI*D.T
        A[-1,-1] /= mesh.vol[-1] # Remove null space
        rhs = np.zeros(mesh.nC)
        txind = Utils.meshutils.closestPoints(mesh, pts)
        rhs[txind] = np.r_[1,-1]
        return A, rhs

    pts = np.vstack((np.r_[0.25, 0.5], np.r_[0.75, 0.5]))

    #Step3: Solve DC problem (LU solver)
    AtM, rhstM = DCfun(tM, pts)
    AinvtM = SolverLU(AtM)
    phitM = AinvtM*rhstM

    ArM, rhsrM = DCfun(rM, pts)
    AinvrM = SolverLU(ArM)
    phirM = AinvrM*rhsrM

    if not plotIt: return

    import matplotlib.pyplot as plt

    #Step4: Making Figure
    fig, axes = plt.subplots(1,2,figsize=(12*1.2,4*1.2))
    vmin, vmax = phitM.min(), phitM.max()
    dat = tM.plotImage(phitM, ax=axes[0], clim=(vmin, vmax), grid=True)
    dat = rM.plotImage(phirM, ax=axes[1], clim=(vmin, vmax), grid=True)
    cb = plt.colorbar(dat[0], ax=axes[0]); cb.set_label("Voltage (V)")
    cb = plt.colorbar(dat[0], ax=axes[1]); cb.set_label("Voltage (V)")

    axes[0].set_title('TensorMesh')
    axes[1].set_title('CurvilinearMesh')
    plt.show()


if __name__ == '__main__':
    run()