Re: GEANT-3 grkuta

Andre,

I am afraid that this change is not sufficient to transport particles backward.
For example the energy must be increased and not decreased. We had a specialized program called geantE to do this.

Rene

Andre Lebedev wrote:
> Hello,
>
> To transport a particle backward I either switch the sign of momentum
> and direction cosines or the sign of step. If I'm not mistaken, the
> two are mathematically equivalent, and I was trying to do the latter,
> hence found the bug.
> Of course, for the purpose of simulation the step is always positive,
> but in case of reconstruction, it may be negative.
>
> Regards,
> Andre.
>
> Victor Perevoztchikov wrote:
>> Hi Andre,
>>
>>> - Speed of light is 299,792,510 instead of 299,792,458 (PDG value)
>>>
>> you are right, but:
>> - we never know mag field with accuracy better 1e-6
>> - grkuta is estimation, neglecting energy loss, multiple scatterring,
>> etc...
>> So it is no important.
>>
>>
>>> - In line 110 comparison "IF (EST.GT.H)" assumes that H is positive,
>>>
>> H is always positive. It is a step in direction of particle momentum.
>>
>>
>>> while if I'm not mistaken it doesn't have to be (and elsewhere
>>> comparison is always to abs(h))
>>>
>> You right, abs(H) is redundant.
>>
>> Victor
>>
>>
>> Victor M. Perevoztchikov perev_at_bnl.gov
>> Brookhaven National Laboratory MS 510A PO Box 5000 Upton NY 11973-5000
>> tel office : 631-344-7894; fax 631-344-4206;
>>
>> ----- Original Message -----
>> From: "Andre Lebedev" <lebedev_at_fas.harvard.edu>
>> To: <vmc_at_pcroot.cern.ch>
>> Sent: Monday, November 27, 2006 7:09 PM
>> Subject: [VMC] GEANT-3 grkuta
>>
>>
>>
>>> Hello.
>>>
>>> I've noticed 2 minor issues with GEANT3 Runge-Kutta stepper
>>> - Speed of light is 299,792,510 instead of 299,792,458 (PDG value)
>>> - In line 110 comparison "IF (EST.GT.H)" assumes that H is positive,
>>> while if I'm not mistaken it doesn't have to be (and elsewhere
>>> comparison is always to abs(h))
>>>
>>> Neither is a show stopper, but given the fact that G3 is still sort of
>>> supported in the realm of virtual MC, you may be in a good position to
>>> address these bugs.
>>>
>>> Best regards,
>>> Andre.
>>>
>>>
Received on Wed Nov 29 2006 - 09:39:26 MET