[mcstas-users] switchable components (WHEN) problem

[Emmanuel FARHI]

Hello Jean-Francois,

Thanks for the special Barbapapa instrument file, which I should think
about including in the McStas package ;-) .

The declaration of variables can only be initialized to constants in
DECLARE. For other assignements, use the INITIALIZE:

DECLARE

  int NOK9_type=0;

INITIALIZE

  NOK9_type = NOK9_Type;


Cheers, Emmanuel.


On Wed, June 22, 2011 20:43, Jean-Francois.Moulin at hzg.de wrote:
> Hi dear McStas Team!
>
> first of all I wanted to send you a big thanks for the NIDS school in Lund
> !
> You got me started!
>
> Now... I of course come with some questions...
> First one is related to the use of facultative components built using a
> WHEN.
>
> I 'd like to be able to activate them via an INSTRUMENT parameter (which I
> understand is out of scope in the WHEN).
>
> This is what I did:
>
> DEFINE INSTRUMENT REFSANS(... foo, bar.....
>                                                   int NOK9_Type = 0 )
>         /* My switch*/
>
> DECLARE
> %{
>
>         int NOK9_type = NOK9_Type; */ copied here to put it in WHEN scope
> */
> ...
> %}
>
> .... long list of components...
>
> /*  In order to keep a reference to a switchable device I use an arm */
> COMPONENT NOK9 = Arm()
>     AT (0, 0, l_NOK8 + space_NOK89) RELATIVE NOK8
>
> /* first switchable */
> COMPONENT NOK9_guide = Guide_gravity(w1 = .112, ...., ) WHEN (NOK9_type ==
> 0)
>
>     AT (0, 0, 0) RELATIVE NOK9
> ....
>
> This code fails miserably with:
> /home/jfmoulin/McStas/refsans_chopper_all_noks_switchable.instr:50: error:
> initializer element is not constant
> (line 50 is the declare where I copy the instrument par...)
> I understand that the compiler expects the declare to be constants but I
> thought this followed the tip given in the manual ....
>
> As an additional remark, the manual references Neutron
> site/ILL/ILL_TOF_Env as an example... but this file does not exist on my
> install.
>
> Thanks a lot for any input
> Cheers Jean-Francois
> -
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>
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-- 
FARHI Emmanuel <farhi at ill.fr>
Groupe DS/CS, ILL4/156, Tel 04 76 20 71 35
ILL, Grenoble