general question

[mehrosadate...@gmail.com]

Hello.

I have a general question about codes in qutip.
what is the exactly role of second number in line  5 in my code ( I mean  1000 in taus=np.linspace(0,1000,8000) )?
my code is in this way:

from qutip import *
import matplotlib.pyplot as plt
import numpy as np
N=25
taus=np.linspace(0,1000,8000)
a=tensor(identity(2),destroy(N))
sz=tensor(sigmaz(),identity(N))
sm=tensor(sigmam(),identity(N))
g=2*np.pi*33.9*0.001
H=g*a.dag()*a+g*0.5*sz+g*(sm.dag()*a+sm*a.dag())+(5.76*0.001)*(a+a.dag())
c_ops=[np.sqrt(2*np.pi*4.1*0.001)*a,np.sqrt(2*np.pi*2.6*0.001)*sm]
corr=coherence_function_g2(H,taus,c_ops,a)
plt.plot(np.real(corr),lw=1.5,ls='-')
plt.xlabel(r'$\tau(ns)$',fontsize=20,fontweight='bold')
plt.ylabel(r'$g^{(2)}(\tau)$',fontsize=20,fontweight='bold')
plt.show()

Regards
Mehrosadat

[Andrew Dawes]

https://docs.scipy.org/doc/numpy/reference/generated/numpy.linspace.html

The parameters are start,stop,num where num is number of points

Sent from my phone using voice-recognition software and/or clumsy thumbs, please forgive any typos.

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[mehrosadate...@gmail.com]

Dear Dr.Dawes,

I am really confused !
Because the result of my code shows another things.  As you can see from attached figure, It shows that the parameters are start, num and stop !!!
what is the correct answer?


Regards
Mehrosadat

[Paul Nation]

You are plotting only the y values..

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[Andrew Dawes]

This overview of the plotting commands may be useful. It covers many of the questions you have asked about plots and settings:

http://matplotlib.org/users/pyplot_tutorial.html

Specifically, as Paul said, you aren't actually plotting g(2) vs t, you are plotting g(2) only so the values go from 0,8000 because there are 8000 of them in the array. You want to put your time array in the plot function too.

Sent from my phone using voice-recognition software and/or clumsy thumbs, please forgive any typos.

[mehrosadate...@gmail.com]

1) Do mean that 1000 is  unnecessary , and putting taus=np.linspace(0,8000) is enough ?

If we do that, we will receive another result !!!

2) How can we be sure that the selected number of points (num) is true?

Regards

Mehrosadat

[Paul Nation]

You need all three. 0 is the start number, 1000 is the end, and 8000 is how many steps you take from start to end.

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[Andrew Dawes]

No, the change needs to be in the plot command. Make it:

plt.plot(taus,np.real(corr),lw=1.5,ls='-')

That way 'taus' is your x value (time) and 'np.real(corr)' is the y value. If you only put one array in the plot function it plots the values against the position within the array. If you want a graph of y vs t then you have to give the t array and the y array (and they have to be the same length). Please look through the plotting tutorial, it answers all of these questions quite clearly.

Sent from my phone using voice-recognition software and/or clumsy thumbs, please forgive any typos.

On Nov 12, 2016, at 7:05 PM, mehrosadate...@gmail.com wrote:

plt.plot(np.real(corr),lw=1.5,ls='-'