Yes, that sounds reasonable. I simply lagging behind the development and need to catch up in how we do things. I emailed Richard and Freddy on the side about some stuff.

But when you brought it up, is there a documentation on the replacement mechanism? In the email to R&F I also suggested a README in Artscat, to clarify the content in the folder.



On 2021-09-20 11:10, Stefan Buehler wrote:
Dear Patrick,

I think we should put ARTS’ own line catalog in the center wherever possible 
(which is based on converted current HITRAN). Use it, if you are happy with the 
parameters there. If you want other parameters, and there is a good reason for 
that, consider updating it. We have a mechanism to replace individual 
parameters there (and document those substitutions).


On 20 Sep 2021, at 10:46, Patrick Eriksson wrote:


Thanks for additional information. Seems that the take home message is that I 
should look at other ways to set up the calculations. I just picked up an old 
cfile, used that as a starting point and did not even consider alternatives to 
use ReadHITRAN.



On 2021-09-20 09:05, Richard Larsson wrote:
Hi Patrick,

We can of course optimize the reading routine but there's no point in doing 
that.  The methods that read external catalogs should only ever be used once 
per update of the external catalog, so it's fine if they are slow but not too 

New memory is allocated for every absorption line always.  This is because we 
keep line data local, and the model for the line shape and the local quantum 
numbers don't have to be known at compile-time.

Additionally, the line data is pushed into arrays, so they will double in size 
every time you reach the current size.

If we knew the number of lines and broadening species and local quantum 
numbers, then these allocations happen once for the entire band, but we don't 
in ReadHITRAN or any of the external reading routines.  So you will have 
many-many system calls asking for more memory.  This of course also means that 
you are over-allocating memory since that's how Arrays work in ARTS (because 
that's standard C++).  Again, this is also fine since the external catalog when 
read again will allocate only exactly what is required.

With hope,

Den mån 20 sep. 2021 kl 08:09 skrev Patrick Eriksson < 
<>> :


     Thanks for the clarification.

     Is the allocation of more memory done in fixed chunks? Or something
     "smart" in the process? If the former and the chunks are too small,
     maybe I am doing a lot of reallocations. My impression was that memory
     usage increased quite monotonically, not in noticeable steps.

     If the lines have to be sorted into bands, then the complexity of the
     reading will increase in line with what I have noticed. And likely not
     much to do about it.



      > There are two possible slowdowns there could be still. One is
     that you
      > hit some line count where you need to reallocate the array of lines
      > because you have too many. The other is that the search for
     placing the
      > line in the correct band is slow when there are more bands to
     look through.
      > The former would be just pure bad luck, so there's nothing to do
     about it.
      > I would suspect the latter is your problem.  You need to search
      > the existing bands for every new line to find where it belongs.     
      > bands are often clustered closely together in frequency, this
     could slow
      > down the reading as you get more and more bands. A smaller frequency
      > range means fewer bands to look through.
      > //Richard
      > On Sun, Sep 19, 2021, 22:39 Patrick Eriksson
      > <
     <>>> wrote:
      >     Richard,
      >      > It's expected to take a somewhat arbitrary time.  It reads
      >     I have tried multiple times and the pattern is not changing.
      >      > The start-up time is going to be large because of having
     to find the
      >      > first frequency, which means you have to parse the text
      >     Understood. But that overhead seems to be relatively small.
     In my test,
      >     it seemed to take 4-7 s to reach the first frequency. Anyhow,
     this goes
      >     in the other direction. To minimise the parsing to reach the
      >     frequency, it should be better to read all in one go, and not
     in parts
      >     (which is the case for me).
      >     Bye,
      >     Patrick

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