# Tutorial on Numerical Methods for Fiber Optics Gain Simulator by Using Python #Tutorial-7

in utopian-io •  last year

#### What Will I Learn?

This tutorial covers the topics on scientific calculations such as integration, derivatives and interpolation by using scipy.integrate, scipy.misc and scipy.interpolate packages. Before continuing the previous tutorial which is about Fiber Optics Gain Simulator, we need to learn these calculations.

• You will learn integration by using scipy.integrate package.
• You will learn derivatives by using scipy.misc package.
• You will learn interpolation by using scipy.interpolate package.

#### Requirements

• Windows 8 or higher.
• Python 3.6.4.
• PyCharm Community Edition 2017.3.4 x64.
• Importing numpy, scipy, matplotlib packages

#### Difficulty

This tutorial has an indermadiate level.

#### Tutorial Contents

First of all, you need to import numpy, scipy, matplotlib, packages for this tutorial. To import these packages you can check our previous tutorials such as here. After importing the packages we need to call the packages which will be used in the program such as:

``````import numpy as importing
from scipy.integrate import *
from scipy.interpolate import interp1d
from scipy.misc import derivative
import matplotlib.pyplot as plotting
``````

Let's start with integration. For numerical calculations, there are lots of types of interpretations of the integral such as Riemann–Darboux's integration, Lebesgue integration, trapezoidal and also quad one. This tutorial wil cover darboux, trapezoidal and quad integration and we will see the difference of these two integration types.

First of let's create a function such as:

``````func=lambda x:3*x**2
x=importing.linspace(0,10,1000)
plotting.plot(x, func(x))
plotting.xlabel("x (a.u.)")
plotting.ylabel("func (a.u.)")
plotting.show()

``````

This is the graph of 3x2 function for x between 0 and 10:

Let's write a code for numerical solution for darboux, trapezoidal methods such as:

``````func=lambda x:3*x**2

limitD=0
limitH=10
n=1000

hDarboux=(limitH-limitD)/n
hTrapezoidal=(limitH-limitD)/n

Eqn1=(func(limitD)+func(limitH))
for i in range(1,n):
Eqn1=func(limitD+i*hDarboux)+Eqn1
#Eqn+=f(a+i*h)
IntegralSolutionDarboux=hDarboux*Eqn1

Eqn2=0.5*(func(limitD)+func(limitH))
for i in range(1,n):
Eqn2=func(limitD+i*hTrapezoidal)+Eqn2
#Eqn2+=f(a+i*h)
IntegralSolutionTrapezoidal=hTrapezoidal*Eqn2

print(IntegralSolutionDarboux)
print(IntegralSolutionTrapezoidal)
``````

The results are:

``````1001.5005000000004--IntegralSolutionDarboux
1000.0005000000008--IntegralSolutionTrapezoidal
``````

As you see that if you divide your graph into 1000 elements then the result has a some errors. For Darboux method the error is almost 0.15% and for trapezoidal method, the error is almost 0.00005%. However, quad method is the best for integration method which will give you an error below 10-10%. Let's check:

``````print(quad(func,limitD,limitH))
``````

The result:

``````(1000.0000000000001, 1.1102230246251567e-11)
``````

As you see there are result. First element is the result and the second one is the error. You can take these data for different variables such as:

``````result, error=(quad(func,limitD,limitH))
print(result)
print(error)
``````

For quad method you will write like this, quad(function, first limit, second limit).
As a result for trapezoidal or Darboux methods will be good for imported data. Because for imported data you cannot define your difference of the x element for f(x). But for just calculations you can use quad subpackage easily.

Let's move on derivatives. First of all, create a function:

``````func2=lambda x:x**3
x=importing.linspace(0,10,1000)
plotting.plot(x,func2(x))
plotting.xlabel("x (a.u.)")
plotting.ylabel("func2 (a.u.)")
plotting.show()
``````

This is the graph of x3 function for x between 0 and 10:

Then let's take the first derivative of this function such as:

``````print(derivative(func2,10,dx=1e-10))
``````

To see on graph:

``````func2=lambda x:x**3

a=[]
print(derivative(func2,10,dx=1e-10))
x=importing.linspace(0,10,1000)
for i in range(1,len(x)):
a.append(int(derivative(func2,x[i],dx=1e-10)))
plotting.plot(x,func2(x),label="func2")
plotting.plot(x[0:999],a,label="derivative of func2")
plotting.xlabel("x (a.u.)")
plotting.legend()
plotting.show()
``````

The result:

As you see that the derivative method is used like this, derivative(function, x=, dx=error).

Let's move on interpolation. In this tutorial we will examine three different interpolation method such as linear, quadratic and cubic such as:

``````x=importing.linspace(0,10,10)
y=10*importing.random.randn(10)
plotting.plot(x,y,'bo',label='Real Data')

xLinear=importing.linspace(0,10,100)
yLinear=interp1d(x,y,kind='linear')
plotting.plot(xLinear,yLinear(xLinear),'r',label='Linear Interpolation')

xCubic=importing.linspace(0,10,100)
yCubic=interp1d(x,y,kind='cubic')
plotting.plot(xCubic,yCubic(xCubic),'g',label='Cubic Interpolation')
plotting.legend()
plotting.show()
``````

The result is :

The usage is like this. For interp1d method we need to create a new array for interpolation (higher number of array means higher resolution). Then we need to make a interpolation for real data such as yMethod=interp1d(real x data, real y data, kind='method'), method can be 'linear', 'quadratic' or 'cubic'. yMethod is a just a function and we can define our variables such as yMethod(new x data). Then we have interpolated data.

In this tutorail we learnt how to take integration, derivatives and interpolation and gave some graphical examples on these topics by using matplotlib.pyplot package.

#### Curriculum

Here is the list of related tutorials we have already shared on @utopian-io community.

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