hi Matt & all,
I just had a query from one of my users which prompted me to see if any
progress had been made on the issue below - using PETSc to get the
number of time steps in an HDF5 file.
I can't see anything new in PETSc on this - I did try using
PetscViewerHDF5ReadSizes() to see if that would do it, but it seems it
doesn't. If I use that on the "time" dataset it just returns 1.
Regards, Adrian
On 11/10/21 2:08 pm, Adrian Croucher wrote:
On 10/11/21 11:59 AM, Matthew Knepley wrote:
On Sun, Oct 10, 2021 at 6:51 PM Adrian Croucher
<a.crouc...@auckland.ac.nz> wrote:
hi
Is there any way to query the PETSc HDF5 viewer to find the
number of
time steps in the file?
A common use case I have is that an HDF5 file from a previous
simulation
is used to get initial conditions for a subsequent run. The most
common
thing you want to do is restart from the last set of results in the
previous output. To do that you need to know how many time steps
there
are, so you can set the output index to be the last one.
I thought maybe I could just query the size of the "time"
dataset, but I
can't even see any obvious way to do that using the viewer functions.
There is nothing in there that does it right now. Do you know how to
do it in HDF5?
If so, I can put it in. Otherwise, I will have to learn more HDF5 :)
I haven't actually tried this myself but it looks like what you do is:
1) get the dataspace for the dataset (in our case the "time" dataset):
hid_t dspace = H5Dget_space(dset);
2) Get the dimensions of the dataspace:
const int ndims = 1;
hsize_t dims[ndims];
H5Sget_simple_extent_dims(dspace, dims, NULL);
The first element of dims should be the number of time steps. Here
I've assumed the number of dimensions of the time dataset is 1. In
general you can instead query the rank of the dataspace using
H5Sget_simple_extent_ndims() to get the rank ndims.
Regards, Adrian
--
Dr Adrian Croucher
Senior Research Fellow
Department of Engineering Science
Waipapa Taumata Rau / University of Auckland, New Zealand
email:a.crouc...@auckland.ac.nz
tel: +64 (0)9 923 4611
