#print "IV file is: ",filename

formula="(dI/dV)/(I/V)"

# reading data

f = open(filename)

lines = f.readlines()

# writing data in lists

V = []

I = []

for line in lines:

tmp = line.split()

v = float(tmp[0])

i = float(tmp[1])

if ( v == 0 ):

continue

V.append(v)

I.append(i)

# closing file

f.close()

# from lists to array

V = np.asarray(V)

I = np.asarray(I)

# creating an interporlation of the IV curve

#interpolation_of_iv = interpolate.splrep(V, I,k=5)

#interpolated_I = interpolate.splev(V,interpolation_of_iv,der=0)

# plot a comparison

#plt.figure()

#plt.plot(V, I, 'xb',V,interpolated_I,'-r')

#plt.legend(['Data','Interpolation'],loc=6)

#plt.xlabel('Vbias [V]')

#plt.ylabel('Ileak [nA]')

#plt.yscale('log')

#plt.title('IV, W93, S1')

#plt.show()

# calculating log and derivative

#interpolated_I = np.asarray(interpolated_I)

#print interpolated_I

index = 0

logI = []

for I in I:

logi = mathlog(I)

#print V[index],I,logi

logI.append(logi)

index = index + 1

logI = np.asarray(logI)

#logI = np.log(interpolated_I)

interpolation_of_iv = interpolate.splrep(V, logI,k=5)

dlogIdV = interpolate.splev(V,interpolation_of_iv,der=1)

#observable_values = 1.0/dlogIdV

v_bd = 0

one_over_dlogIdV = 1.0/dlogIdV

v_bd = V[np.argmax(dlogIdV)]

#v_bd = V[np.argmin(one_over_dlogIdV)]

#print "Breakdown voltage is:", v_bd,"V"

# returning the interpolated current

#return interpolated_I