Directory:
    ${PENCIL_HOME}/samples/testfield_z
SVN Id:
    $Id$
Maintainer:
    Axel Brandenburg <brandenb/nordita[dot]dk>
Added:
    26-Jun-2005
Status:
    New reference data since 13 April 2008.
Recommended resolution:
    32x32x32 with etatest=5e-2 works fine.
Comments:
    This procedure allows the full alpha and eta tensors to be calculated.
    Different test fields can be used. Note however that the result is
    in general wavenumber dependent. The present example is for the
    homogeneous helical turbulence with large-scale uniform shear.
    By setting itestfield='B11-B22_lin', we can use constant and linear
    test fields. Their profiles can be analysed with
    IDL> .r pc_read_alpha_xyaver . Further examples can be found in
    http://www.nordita.org/~brandenb/teach/PencilCode/material/RobertsTestfield
References:
    Brandenburg, A.: 2005, ``Turbulence and its parametrization in
       accretion discs,'' Astron. Nachr. 326, 787-797
    Brandenburg, A., Radler, K.-H., Rheinhardt, M., & Kapyla, P. J.:
       2008, ``Magnetic diffusivity tensor and dynamo effects in
       rotating and shearing turbulence,'' Astrophys. J. 676, 740-751