# Are vtables actually needed?

**URL:** <https://forum.ecmwf.int/t/are-vtables-actually-needed/12187>\
**Category:** OpenIFS\
**Tags:** openifs-configuration-and-namelists, openifs-ifsdata\
**Created:** [19 February 2021 14:59 UTC](https://forum.ecmwf.int/t/are-vtables-actually-needed/12187 "2021-02-19T14:59:25Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Joakim\_Kjellsson](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@Joakim\_Kjellsson](https://forum.ecmwf.int/u/Joakim_Kjellsson)\
**Post date:** [19 February 2021 14:59 UTC](https://forum.ecmwf.int/t/are-vtables-actually-needed/12187/1 "2021-02-19T14:59:25Z")

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Hi all

I always link rtables and vtables folders in my run directory when I run OpenIFS, but I just tried to run without vtables and it still works.

I've dug into the code and I can't find that vtable files, e.g. vtable\_L137, is ever read by OpenIFS.

Are the A,B coefficients for the vertical grids set from the initial conditions? Or what controls these parameters?

Many thanks  
 Joakim

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**Author:** ![Glenn\_Carver](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/g/e495f1/32.png) [@Glenn\_Carver](https://forum.ecmwf.int/u/Glenn_Carver)\
**Post date:** [19 February 2021 16:52 UTC](https://forum.ecmwf.int/t/are-vtables-actually-needed/12187/2 "2021-02-19T16:52:48Z")

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Hi Joakim,

Not sure why you link to the vtable directory, the oifs\_run script doesn't?

The model doesn't need it to run, it gets it's horizontal and vertical grid from the initial files. The vtables are there for other programs that might need them for vertical interpolation etc, just for completeness.&nbsp; The rtables are a different matter, they are needed because the radiation scheme can run on a different horizontal grid to the dynamics.

Cheers,&nbsp; Glenn

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**Author:** ![Joakim\_Kjellsson](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/j/e19b73/32.png) [@Joakim\_Kjellsson](https://forum.ecmwf.int/u/Joakim_Kjellsson)\
**Post date:** [22 February 2021 08:54 UTC](https://forum.ecmwf.int/t/are-vtables-actually-needed/12187/3 "2021-02-22T08:54:22Z")

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Hi Glenn

Good to know. I guess I just assumed that everything from the ftp server was necessary, so I just linked everything and never thought much more about it. Then I know I can safely stop linking it.&nbsp;

Cheers  
 Joakim

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**Author:** ![Glenn\_Carver](https://forum.ecmwf.int/letter_avatar_proxy/v4/letter/g/e495f1/32.png) [@Glenn\_Carver](https://forum.ecmwf.int/u/Glenn_Carver)\
**Post date:** [22 February 2021 12:39 UTC](https://forum.ecmwf.int/t/are-vtables-actually-needed/12187/4 "2021-02-22T12:39:42Z")

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Check against what the bin/oifs\_run script does if you write your own run script. oifs\_run in turn was based on our internal run script for IFS.