[MITgcm-support] Barotropic ocean gyre tutorial

Sun Apr 4 09:00:32 EDT 2021

Dear Oliver,

Thanks for coming back to me. I did just that. I now get a plot for "eta"
that appears to be two sets of constant values, on the left and right of
the line x=0.6*1e6 m (see the attached plot in
fig_bar_gyre_windx_siny.png). I also notice that the output bin file
(tau_2_1) still shows different values to the original numpy array (tau_2).
I have attached the latest version of the python script used to generate
the data (gendata_tut4.1.py) and the script used to generate the plots (
tut_4.1_plots.py).

Best
Jeremy

On Sun, 4 Apr 2021 at 13:48, Oliver Jahn <jahn at mit.edu> wrote:

> Hi Jeremy,
>
> this will not work:
>
> > if sys.byteorder == 'little': tau_2.byteswap(True)
> > fid = open('windx_siny.bin', 'wb')
> > tau_2.astype('float32').tofile(fid)
>
> Can you instead try Jeff's suggestion:
>
> tau_2.astype('>f4').tofile('windx_siny.bin')
>
> and NOT use the byteswap command?  Mixing byteswap and astype is a bad
> idea as byteswap will create a mismatch between the data in memory and
> numpy's assumption of the data type.
>
> Best,
> Oliver
>
>
> > as you suggested, the plot still came out blank.
> > Regarding Jeffrey Scott's comment that the reason I could not read back
> > the bin file was due to a mismatch between float32 and float64, I
> > followed his advice and read in the
> > bin file using the snippet
> >
> > tau_2_1 = np.fromfile('windx_siny.bin',dtype='float32')
> >
> > and I got back an array with every entry being 'inf' except the
> > penultimate column, being all '0'.
> >
> > Is it possible that the snippet
> >
> > # X=X.astype('float128')
> > # Y=Y.astype('float128')
> >
> > (which is commented) needs to be included but with 'float128' replaced
> > with 'float32'?
> >
> > Best
> > Jeremy
> >
> >
> >
> >
> >
> > On Thu, 1 Apr 2021 at 16:47, Jan Klaus Rieck <jan.rieck at mail.mcgill.ca
> > <mailto:jan.rieck at mail.mcgill.ca>> wrote:
> >
> >     Hello Jeremy Miller,
> >
> >     I also use python to to generate input data for the MITgcm. I found
> >     that, to generate files that can be read by the MITgcm consistently,
> >     I needed to specify the type explicitly.
> >     My way of saving the files would look like this in your case:
> >
> >     if sys.byteorder == 'little': tau_2.byteswap(True)
> >     fid = open(''windx_siny.bin', 'wb')
> >     tau_2.astype('float32').tofile(fid)
> >
> >     Of course, 'float32' could be replaced by 'float64' if you require
> >     double precision.
> >
> >     I hope this helps,
> >     Jan Rieck
> >
> >     On Thu, 2021-04-01 at 10:22 +0300, Jeremy Miller wrote:
> >>     Dear MITGCM forum,
> >>
> >>     I am Jeremy Miller, I am new to MITgcm and I've been going through
> >>     the tutorials. I have a question about the "Barotropic Ocean Gyre"
> >>     tutorial (section 4.1).
> >>
> >>     I managed to compile and run the code, and re-produce the first
> >>     two plots shown in section 4.1.5 for  wind stress of τ = τ0 cos(
> >>     πy/Ly), for both the advection and non-advection cases (with the
> >>     provided input binary files).
> >>     I ran into problems when trying to produce the third plot, for the
> >>     case where τ = τ0 sin( πy/Ly). I am a python user, so I translated
> >>     gendata.m into python to write the input binary
> >>     files 'windx_cosy.bin' 'windx_siny.bin' (see the file
> >>     gendata_tut4.1py attached).  As explained in section 3.9 I've
> >>     included the snippet
> >>
> >>     if sys.byteorder == 'little': tau_2.byteswap(True)
> >>
> >>     where "tau2" is the array to be output. There was no issue in the
> >>     cosine wind stress, and I managed to reproduce the results that I
> >>     got with the original 'windx_cosy.bin' provided in the tutorial.
> >>     However, with the sine wind stress case, the output in
> >>     'Eta.0000077760.001.001' is all zeros.
> >>
> >>     When I attempt to read  'windx_siny.bin' with python into a new
> >>     array called tau2_1. I get absurdly big numbers back, which do not
> >>     match the original array tau2 that I created. If I Remove the
> >>     snippet " if sys.byteorder == 'little': tau_2.byteswap(True) ", in
> >>     the python gendata code, tau2_1 and tau2 match. But, then when I
> >>     run the code again, the file output.txt contains a long list of
> NaNs.
> >>
> >>     I have also included the python code used to generate the plots in
> >>     the file tut_4.1_plots.py <http://tut_4.1_plots.py/>
> >>
> >>     Look forward to hearing from you.
> >>     Yours sincerely
> >>     Jeremy Miller
> >>     _______________________________________________
> >>     MITgcm-support mailing list
> >>     MITgcm-support at mitgcm.org
> >>     <mailto:MITgcm-support at mitgcm.org>
> >>
> >>     http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support
> >>
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