Painting to grid file and reading from a grid file

[rainwoodman]

No description provided.

[rainwoodman]

I am guessing we still need an example to finalize this?

[nickhand]

yeah I think so. Maybe we could incorporate it into a caching system (see #98)? Would be useful for reading cached painted fields

[rainwoodman]

I still want to finalize a 'format'.

In the end I think we'd like to have a routine that decomposes (complex, ravelled_index) to a PM's complex buffer.

I yet have to decide the format of the fastpm deltak field. I have a very mixed hate/love feeling on the current version. Take a look and what do you think?

https://github.com/rainwoodman/fastpm/blob/master/python/fastpm.py#L4

The biggest issue is the number of files is per rank and can get pretty bad on large runs. @aslanyan already suffer from this quite a bit - it takes several minutes to remove a folder.

[rainwoodman]

This is replaced by #221