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    Hi all,<br>

    <br>

    I am trying to compare the energy between two datasets. I execute

    the following script that uses the derived field 'RelativeEnergy':<br>

    <br>

    <address>--------------------------------------------------------------------------------------------------------------------------------------------------</address>

    <address>def _RelativeEnergy(field, data):</address>

    <address>    return

(data["TotalEnergy"]-data.pf.parameters["TotalEnergy_ref"])/data.pf.parameters["TotalEnergy_ref"]</address>

    <address>add_field("RelativeEnergy", function=_RelativeEnergy)</address>

    <address><br>

      filen1 = 'helix/DD0000/CE0000'</address>

    <address>pf1 = load(filen1)</address>

    <address>region1 = pf1.h.region([0.5, 0.5, 0.5], [0.0, 0.0, 0.0],

      [1.0, 1.0, 1.0])</address>

    <address>energy1 = region1["TotalEnergy"]</address>

    <address><br>

      filen2 = 'parallel/DD0000/CE0000'</address>

    <address>pf2 = load(filen2)</address>

    <address>region2 = pf2.h.region([0.5, 0.5, 0.5], [0.0, 0.0, 0.0],

      [1.0, 1.0, 1.0])</address>

    <address>energy2 = region2["TotalEnergy"]</address>

    <address><br>

      # Adding reference energy into

      pf2                                                             </address>

    <address>pf2.parameters["TotalEnergy_ref"] = energy1</address>

    <address><br>

      delta_energy = region2["RelativeEnergy"]</address>

    <address><br>

      pc = PlotCollection(pf2)</address>

    <address>pc.add_slice("RelativeEnergy",2,center=[0.5, 0.5, 0.5])</address>

    <address>pc.set_lim((0.4, 0.6, 0.4, 0.6))</address>

    <address>pc.save('DeltaEnergy')</address>

    <address>

--------------------------------------------------------------------------------------------------------------------------------------------------</address>

    <br>

    I get the error pasted here:

    http://paste.yt-project.org/show/DPgMjV44JktpXExCljUj/<br>

    The variable delta_energy looks good (same type and size and

    energy1), but the problem arises when I try to take a slice of it.<br>

    <br>

    Any help much appreciated.<br>

    Thanks a lot,<br>

    <br>

    JC<br>

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