FITTIN PROCEDURE
----------------

1. Ray tracing through Solenoid magnet
   -> (x,x',y,y') at input and output of simulation z=[-0.5,0.5]
   Data in data.txt

2. Run linfit for producing matrix representation
   ~/Code/linfit/linfit  --infile data.txt --ivarc 4 --polyorder 1 --depcol 0
   ~/Code/linfit/linfit  --infile data.txt --ivarc 4 --polyorder 1 --depcol 1
   ~/Code/linfit/linfit  --infile data.txt --ivarc 4 --polyorder 1 --depcol 2
   ~/Code/linfit/linfit  --infile data.txt --ivarc 4 --polyorder 1 --depcol 3

   Fit to ray-tracing:
   -0.16945  0.272915   -0.169915   0.268352
   -1.75785  -0.172501  -1.72776   -0.165878
   0.169905  -0.268383  -0.169429   0.272935
   1.72775   0.165847   -1.75778   -0.172471

3. Using ~/Code/Linear_optics/fit_solenoid.cpp fit the total matrix for
   drift + solenoid + drift system to the matrix from ray-tracing

   Fitted solenoid model with B0=0.225517, L=0.222328:
   -0.174198     0.272027    -0.171882     0.268411 
     -1.7511    -0.174198     -1.72782    -0.171882 
    0.171882    -0.268411    -0.174198     0.272027 
     1.72782     0.171882      -1.7511    -0.174198 

Why is the length different from int(B^2 dx)/Bmax^2 = 0.130843 m