reset set output "iv_body.svg" set terminal svg set title "Dorcy 41-4001 (body only) driver circuit characterization" set xlabel "Input V" set ylabel "Input i" set grid # from previous fit a = 24.9834 b = -20.1936 c = 4.07537 id(vd) = a + b*vd + c*vd**2 # i = id(vd) # i = (v - vd)/r # # -> a + b*vd + c*vd**2 = v/r - vd/r # -> a + (b + 1/r)*vd + c*vd**2 = v/r # -> c * vd**2 + (b + 1/r) * vd + a-v/r = 0 # -> vd = ( -(b + 1/r) + sqrt( (b + 1/r)**2 - 4*c * (a-v/r)) ) / (2*c) vd(r,v) = ( -(b + 1/r) + sqrt( (b + 1/r)**2 - 4*c * (a-v/r)) ) / (2*c) r=1 fit (x-vd(r,x))/r "iv_body.dat" noerror via r plot "iv_body.dat" with points notitle, (x-vd(r,x))/r notitle