The first one to unsubscribe ?

[Mark Hagen]

Hi Kristian,

I don't know if you keep a watchful eye on who subscribes and unsubscribes
from your mailing list ? If you do you may be insulted to see that 
pha70 at cc.keele.ac.uk (Mark Hagen) has unsubscribed, however I can reassure
you I hope by pointing out that mark.hagen at neutron-server.kek.jp has 
subscribed to it. Easier to get my e-mail here at the moment, rather than
in Keele.

Okay, other reasons for e-mailing. I leave it to you as to whether you forward
these onto the e-mail list or if you quietly deal with them.


The ALLOCA problem.
-------------------
When I was at the MC meeting we tried to compile MCStas on MS-Visual C++, I 
don't know if you recall or not. However the reason it wouldn't work was
because in instrument.tab.c there was a call to alloca, which it seems isn't
an ANSI standard-C function. Okay my reason for bringing this up again is that
I "made a sale" yesterday. A guy from Metro. Univ. in Tokyo who works at KEK.
We tried to install Mcstas on a Hewlett Packard Workstation (HPUX) he has and
it failed because it objected to alloca.

Okay, so the guy will try installing it on an IBM Unix (AIX ?) workstation to
see if it will work through there.

Now you had a work around for the failure of alloca ? using malloc. Any chance 
of version of instrument.tab.c with that work around in it ? My recollection for
Visual C++ was that the alloca and changing strcmpcase to stricase were all that
the problem was there. If you made a change to instrument.tab.c and put the new
file on the webpage for download as an "upgrade" for people who have the alloca 
problem then that would resolve the problem for this release. Well if you put
the files with strcmpcase changed to stricase up as well with a note for HP or 
MS-VC users to download them and replace that would be even better. I know you
put up a .exe for Win95 but the correct source files would be nice. 

The good news, Mcstas works fine under Digital Unix, I loaded it on my Keele DEC
Unix Alpha with no problems. Ditto Slackware Linux, the only subtlety is that one
needs to run the final exe files via ./program for some reason.


Time of Flight, Source Distributions and Energy Monitors
-------------------------------------------------------
As I mentioned above Drew Garret and I were demonstrating Mcstas to someone from
Metro. Univ. and we decided to do a very simple ToF sim. to show him. Source +
Collimator + Energy monitor. Okay so a flat energy distribution from say 5meV
to 100meV. But it wasn't flat in the energy detector. Reason being, as Drew
explained to me, your source emits as a uniform velocity distribution ? In other
words you convert the low and high energy ranges to velocities and then use a 
0 t 1 random number generator in the range of velocities ? Velocity is a funny 
one, it is not particularly used. For reactor people this may not matter but to 
us ToF boys it will be more relevant. I think a source should emit in uniform 
energy steps not velocity. 

When I first saw the curved energy distribution I jumped to a conclusion many
ToF people would, that you hadn't done the ToF to Energy jacobian in the 
energy monitor. This isn't strictly correct but is close to the reason. You're
plotting neutrons/unit of velocity in energy bins, hence the graph has a 1/sqrt(E)
form. If you emitted uniformly in energy it would be neutrons/unit energy against
energy which would be a nice flat line.

So a request for a source that emits uniformly in energy, should be an extremely
minor change, in the next revision ?



The mailing list looks very nice, my man from Metro. Univ. was very impressed and
signed on to it. Another suggestion, for your benefit, well Risoes. On the sign on
page, in the form, ask people to supply their names and normal mail addresses as 
well. When it comes time to write a report for the EU about how wonderful all this
Mcstas work is, you'll be able to supply a list of "Mcstas users" from around the 
world showing what a great success it is. A list of e-mail addresses doesn't have 
the same impact. Also it provides a mailing list for any future MC meetings. If
you're unsure about this ask Kurt what he thinks, I think he'll see the "political"
advantages to keeping such a record. Also record the number of hits and downloads
from the web page. Again will look nice and impressive in a report to Brussels in
the future.


Okay, after all these suggestions of work for you I'd better get on and do some of
my own work :) By the way Drew will be in touch soon, he has a working Mcstas routine
for a Fermi chopper. I have one for my program as well. You could mention this to 
Kurt, he asked a number of people at the meeting if they had Fermi chopper code and
everyone said no. Fermi chopper will be a very useful addition, very important for
time of flighters.


Cheers,


Mark