Bdtyktl

My Python 2.7 code that I've been running in Ubuntu 16.04 does some simple graphics plotting routines that provide distorted and unusable plots now that I've upgraded to Ubuntu 18.04. I get no error messages or warnings. I'm NOT running python3 in the new Ubuntu and the version I'm invoking is python version 2.7.15rcq. Any suggestions?

The Python libraries that are imported are:

  scipy

  pylab

  math

and a couple that probably aren't relevant to this plotting problem.

Python IDE for scientists (spyder) can do inline plotting. To try out this feature open the terminal and type:

sudo apt install python2.7 ipython python-matplotlib spyder  

After the ipython prompt in the IPython console copy/paste the below code and press the Enter key to run it.

import matplotlib.pyplot as plt   

x, y = [-1, 12], [1, 4]  

plt.plot(x, y, marker = 'o')  

If that works try the following Python code which uses scipy, pylab and math modules.

import pylab as plb

import matplotlib.pyplot as plt

from scipy.optimize import curve_fit

from scipy import asarray as ar,exp

import math



x=ar([37,69,157,238,274,319,391,495,533,626,1366,1855,2821,3615,4130,4374,6453,6863,7021,

    7951,8646,9656,10464,11400])

y=ar([1.77,1.67,1.65,1.17,1.34,1.46,0.75,1,0.8,1.02,0.65,0.69,0.44,0.44,0.55,0.43,0.75,0.27,0.26,

    0.44,0.04,0.44,0.26,0.04])



n = 24                                  # the number of data

mean = sum(x*y)/n                       # note this correction

sigma = math.sqrt(sum(y*(x-mean)**2)/n) # note this correction



def gaus(x,a,sigma):

    return a*exp(-(x)**2/(2*sigma**2))



p0 = [1.2, 4000]

popt,pcov = curve_fit(gaus,x,y,p0=p0) 



plt.plot(x,y,'b+:',label='data')

plt.plot(x,gaus(x,*popt),'ro:',label='fit')

plt.legend()

plt.title('Fig. 3 - Fit for Time Constant')

plt.xlabel('Time (s)')

plt.ylabel('Voltage (V)')

plt.show()



def gaus(x,a,sigma):

    return a*exp(-(x)**2/(2*sigma**2))



p0 = [1.2, 4000]

popt,pcov = curve_fit(gaus,x,y,p0=p0)

The output is shown in the below screenshot.

^{(Click image to enlarge)}

The output shows this warning:

Warning: pylab (numpy and matplotlib) and symbolic math (sympy) are both 

enabled at the same time. Some pylab functions are going to be overrided by   

the sympy module (e.g. plot).  

... but the plot is output correctly despite this warning message.

In order to eliminate the warning message remove the import pylab as plb at line 1 from the code. Clicking the triangular icon to the left of line 1 shows the following syntax checking message.

'pylab as plb' imported but unused  

The syntax checking message is correct. The code outputs exactly the same plot when line 1 is removed. Sometimes it helps to use an IDE when debugging lengthy blocks of code because an IDE has features like syntax checking.