H5Part development and discussion

[Achim Gsell <achim.gsell AT gmail.com>]

Hi Jozsef

> On 11 Aug 2016, at 23:23, Jozsef Bakosi <jbakosi AT lanl.gov> wrote:
> 
> Hello,
> 
> I have successfully been using H5Part to write particle data to several 
> time steps.
> 
> Now I would like to do the same but without keeping the file open during 
> time
> stepping, so I'm attempting to open the file using APPEND, but get the 
> following
> error message when I try to call H5PartWriteDataFloat64() with a nonzero 
> error
> code:
> 
> E: H5PartWriteDataFloat64: Timegroup <= 0.
> 
> Here is the sequence that I follow:
> 
> I create the file once during initialization:
> 
>  f = H5PartOpenFileParallel( filename, H5PART_WRITE, MPI_COMM_WORLD);
>  H5PartWriteFileAttribString( f, "Origin", "somestring" );
>  H5PartCloseFile( f );
> 
> Then every iteration I repeat:
> 
> 1. Write Time stamp:
> 
>  f = H5PartOpenFileParallel( filename, H5PART_APPEND, MPI_COMM_WORLD);
>  H5PartSetStep( f, it );
>  H5PartSetNumParticles( f, npar );
>  H5PartCloseFile( f );

In 1. you create a new step, but that’s it. The H5PartSetNumParticles() call 
creates a view on the data, but does not create any dataset. The view will be 
reseted while closing the file.

> 
> 2. Write particle coordinates:
> 
>  f = H5PartOpenFileParallel( filename, H5PART_APPEND, MPI_COMM_WORLD);
>  H5PartWriteDataFloat64( f, "x", xdata );
>  H5PartWriteDataFloat64( f, "y", ydata );
>  H5PartWriteDataFloat64( f, "z", zdata );
>  H5PartCloseFile( f );

This doesn’t work. H5PartOpenFileParallel() does *not* set the time-step to 
the latest (but empty in your case) step in append mode. Append mode does not 
mean, you can append new steps only! In append mode you cannot overwrite 
existing datasets or attributes. But you can add datasets or attributes to 
existing steps *and* you can add new steps. 

Best regards

Achim