reset
#
# Fit kB to V^2/(4B) vs R data.  Below R is called x, and
# y = V^2/(4B), so from error propagation 
# (sigma_y/y) = 2 * (V^2/(4B)) * (sigma_V/V)
#
# In the input file fitData.txt, (edit 2<-->3 as appropriate):
# column 1 is R, 
# column 2 is V^2/(4B) for long cables
# column 3 is V^2/(4B) for short cables
#
relerr_V = 0.02
relerr_y = 2*relerr_V
T = 300.0
y(x) = x*kB*T
kB = 1.e-23
FIT_LIMIT = 1e-10
fit y(x) "fitData.txt" using 1:2:(relerr_y*$2) via kB
#
# plot it
#
set bar small
set xrange [0:1e6]
set yrange [0:6e-15]
set xlabel "R   (Ohms)"
set ylabel "V_{rms}^2/(4B)  (V^2 s)"
set style line 1 lt 1
set style line 2 lt 1 pt 7 ps 0.5
plot "fitData.txt" \
     using 1:2:(relerr_y*$2) \
     title "long cable data" with yerrorbars ls 2, \
     y(x) title "fit" ls 1