[BLAST_ANAWARE] Error in time to position algorithm

From: Douglas Hasell (hasell@MIT.EDU)
Date: Wed Apr 30 2003 - 18:32:19 EDT


Hi,

        Aaron has pointed out an error in the time to position algorithm.

        In order to simplify the algorithm I parameterized the time to
position relationship for super-layer=0 and then used symmetry arguments to
use the same parameterization for super-layer=1. However, I forgot to flip
one symmetry axis.

        So, somewhere in the code (Tong took the code I sent him and
changed it to conform to whatever conventions you are using) there should
be something like this:

float WC_pos_vs_t( int wire, int super, float theta, float bfield, int pm,
                   float t ) {

   ...
   ...
   ...

  // If this is superlayer 1 reverse the wire number and field.

  if( super == 1 ) {
    wire = 2 - wire;
    bfield = - bfield;
  }

        The above lines (or equivalent after Tong changed things) should
also reverse the track angle and look something like this:

  // If this is superlayer 1 reverse the wire number, track angle and field.

  if( super == 1 ) {
    wire = 2 - wire;
    theta = -theta
    bfield = -bfield;
  }

        Could someone please change this in the appropriate place since
Tong is away and let everyone know when it is changed? Thanks.

        Also, Chris, its probably worthwhile redoing the ep analysis as
this will change things.

                                                  Cheers,
                                                          Douglas

26-415 M.I.T. Tel: +1 617 258 7199
77 Massachusetts Avenue Fax: +1 617 258 5440
Cambridge, MA 02139, USA E-mail: hasell@mit.edu



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