lecture 12: es 102 plotting with matplotlib · lecture 12: es 102 plotting with matplotlib...

Lecture 12: ES 102Plotting With Matplotlib

Introduction to Computing

IIT Gandhinagar, India

October 29, 2013

Shivakumar,Bireswar (IIT Gandhinagar) Lecture 12: ES 102 Plotting With Matplotlib October 29, 2013 1 / 22

Simple Plotting

Matplotlib provides the necessary functions for data visualization.pylab is an interface to matplotlib.

import pylab as pl to use matplotlib or from pylab import *.

Matplotlib is generally used in conjunction with numpy.

Numpy is already loaded in pylab and np (so you don’t need import

numpy as np).

This lecture is based on http://scipy-lectures.github.io/

intro/matplotlib/matplotlib.html.

Simple Plotting

numpy as np).

Simple Plotting

numpy as np).

Simple Plotting

numpy as np).

Simple Plotting

numpy as np).

Simple Plot

from py l ab import ∗ # This impo r t s ma t p l o t l i b f u n c t i o n s and numpy as np

X=np . a range(−np . p i , np . p i , 2∗ np . p i /256)# Crea t e s 256 un i fo rmed spaced numbers between −p i to p i

S=np . s i n (X) # cos ( x ) , s i n ( x )p l o t (X, S) #p l o t c r e a t e s an o b j e c t which can be p l o t t e d

x l a b e l ( ’x’ , f o n t s i z e =14, c o l o r=’blue’ ) #l a b e l a x i sy l a b e l ( ’sin(x)’ )t i t l e ( ’Plot of sin(x)’ )show ( ) #This a c t u a l l y p l o t s the graph

L12Programs/simpleplot.py

plot() generates an object that can be plotted.

xlabel(’’),ylabel(’’) labels to the X and Y axis

title(’’) title of the plot

show() actually draws all the plottable objects created.

Simple Plot

Simple plot output

Customizing

from py l ab import ∗

x=np . l i n s p a c e (−np . p i , np . p i , 200 , endpo in t=True )

s = np . s i n ( x )c = np . cos ( x )p l o t ( x , s , c o l o r=’red’ , l i n e w i d t h =1, l i n e s t y l e=’--’ , l a b e l="sine" )p l o t ( x , c , c o l o r=’blue’ , l i n e w i d t h =1.5 , l i n e s t y l e=’-’ , l a b e l="cosine" )l e g end ( l o c=’upper right’ )

show ( )

L12Programs/custom plot.py

linspace(start,end,no of elms,endpoint=True/False):generate no of elms many equally spaced elements from start toend. end will not be included only if endpoint=False.

color color of the curve;linewidth thickness of thecurve;linestyle curve pattern; label set the name of the curve.

legend where to show the names of the curves.

Customizing output

Customizing: Axes Limit, Ticks and Gridimport numpy as npimport py l ab as p l# Note t h i s t ime we a r e impo r t i n g p y l a s b as p l

x=np . l i n s p a c e (−2∗np . p i , 2∗ np . p i , 200 , endpo in t=True )

s = np . s i n ( x )p l . p l o t ( x , s , c o l o r=’green’ , l i n e w i d t h =1, l i n e s t y l e=’-’ )

p l . x l im ( x . min ( ) ∗ 1 . 1 , x . max ( ) ∗ 1 . 1 )p l . y l im ( −1 .1 ,1 .1 )

p l . x t i c k s ([−2∗np . p i , −np . p i , 0 , np . p i , 2∗np . p i ] )p l . y t i c k s ([−1 , −0 .5 ,0 ,0 .5 , +1])

p l . g r i d ( True )p l . show ( )

L12Programs/limticks.py

xlim sets x-axis limit, ylim sets y-axis limit.xticks,yticks puts the ticks in the axes.grid sets a rectangular grid.

Customizing: Axes limit etc.. output

More Customizingimport numpy as npimport py l ab as p l

s = np . s i n ( x )c=np . cos ( x )p l . p l o t ( x , s , c o l o r=’green’ , l i n e w i d t h =1, l i n e s t y l e=’-’ )p l . x l a b e l ( ’angle $\\ theta$ ’ , f o n t s i z e =14, c o l o r=’red’ )p l . y l a b e l ( ’cos($\\ theta$) and sin($\\ theta$)’ )

p l . x t i c k s ([−2∗np . p i , −np . p i , 0 , np . p i , 2∗np . p i ] ,[ r ’-$2\pi$’ , r ’$\pi$’ , r ’$0$’ , r ’$\pi$’ , r ’$2\pi$’ ] )

p l . y t i c k s ([−1 , 0 , +1])

p l . show ( )

L12Programs/latex embed.py

We can embed some LATEXcode in the program to get fancy fonts.

Greek Characters like : α, β, π, θ can be printed

even equations dydx |(x0, y0) can be embedded

p l . y t i c k s ([−1 , 0 , +1])

p l . show ( )

p l . y t i c k s ([−1 , 0 , +1])

p l . show ( )

More customizing : output

Bar Plot

x=np . a r r a y ( [ 1 , 2 , 3 , 4 , 5 , 6 ] )

y=np . a r r a y ( [ 5 , 2 , 7 , 9 , 1 1 , 3 ] )

z=np . random . rand (6)∗10

bar ( x , y , f a c e c o l o r=’blue’ , e d g e c o l o r=’white’ )bar ( x ,−z , f a c e c o l o r=’red’ , e d g e c o l o r=’white’ )

y l a b e l ( ’Barplot ’ )t i t l e ( ’Example of a barplot ’ )show ( )

L12Programs/barplot ex.py

Bar Plot : output

Scatter Plot

n = 256X=np . l i n s p a c e (−2∗np . p i , 2∗ np . p i , n , endpo in t=True )Y = s i n (X)+0.1∗np . random . normal (0 , 1 , n )

print X. shape , Y . shape

s c a t t e r (X,Y)

show ( )

L12Programs/scatter ex1.py

Scatter Plot : output

Polar Plot

axes ( p o l a r=True ) #This i s the on l y change you need to do .

th e t a=np . l i n s p a c e (0 ,2∗ np . p i ,N, endpo in t=True )r a d i i =10∗np . s i n ( t h e t a )r a d i i 2 =2∗ t h e t a

p l o t ( theta , r a d i i , c o l o r=’red’ )

p l o t ( theta , r a d i i 2 , c o l o r=’blue’ )

show ( )

L12Programs/polar ex.py

Polar Plot : output

subplotsfrom py l ab import ∗s u bp l o t ( 2 , 2 , 1 ) # Crea t e s a mat r i x o f 2x2 p l o t sX=np . l i n s p a c e (−1 ,1 ,256 , endpo in t=True )

Y1 , Y2 , Y3 , Y4=X, np . power (X, 2 ) , np . power (X, 3 ) , np . power (X, 4 )

p l o t (X, Y1 , c o l o r=’blue’ , l a b e l=’$x$’ )l e g=l egend ( l o c=’best’ )

s u bp l o t ( 2 , 2 , 2 )p l o t (X, Y2 , c o l o r=’red’ , l a b e l=’$x^2$’ )l e g end ( l o c=’best’ )

s u bp l o t ( 2 , 2 , 3 )p l o t (X, Y3 , c o l o r=’green’ , l a b e l=’$x^3$’ )x l a b e l ( ’x’ )l e g end ( l o c=’best’ )

s u bp l o t ( 2 , 2 , 4 )p l o t (X, Y4 , c o l o r=’black’ , l a b e l=’$x^4$’ )x l a b e l ( ’x’ )l e g end ( l o c=’best’ )

show ( )

L12Programs/subplot ex.pyShivakumar,Bireswar (IIT Gandhinagar) Lecture 12: ES 102 Plotting With Matplotlib October 29, 2013 17 / 22

subplots : output

Plotting Data from FileIn many situations the data to be plotted is in a file.You can read the data, store it in arrays and plot the data.

f o=open ( ’height_weight_data.txt’ )

temp=fo . r e a d l i n e ( )heade r=temp . s p l i t ( )print heade r

x=[]y =[]

for l i n e in f o :temp=l i n e . s p l i t ( )i nd ex=temp [ 0 ]h e i g h t=temp [ 1 ]we ight=temp [ 2 ]x+=[h e i g h t ]y+=[we ight ]

X=np . a r r a y ( x )Y=np . a r r a y ( y )

print X. shapeprint Y. shapep l o t (X,Y, c o l o r=’blue’ , marker=’o’ , l i n e s t y l e=’None’ )x l a b e l ( heade r [ 1 ] )y l a b e l ( heade r [ 2 ] )

show ( )

L12Programs/data plot.pyShivakumar,Bireswar (IIT Gandhinagar) Lecture 12: ES 102 Plotting With Matplotlib October 29, 2013 19 / 22

Data Plot : output

Animation

Use animation package import matplotlib.animation as

animation

Ex1: L12Programs/animate basic example.py

Ex2: L12*Programs/animate double pendulum.py

Practice programs

You are given a function f (x) = x3 + 2x2 + 3x + 1. Plot this functionusing matplotlib when x ∈ [−5, 5] with 512 points. Get the inputfrom the user to give a number x0 between [-2,2]. At the point(x0, f (x0), draw a tangent to this curve. Label the axes and curve.Save the output as a png file.

Suppose f (x , n) =∑n

k=1sin(2π(2k−1)x)

2k−1 . The use will give the value ofn. Plot f (x , n) for that n. See the trend as n increases.

lecture 12: es 102 plotting with matplotlib · lecture 12: es 102 plotting with matplotlib...

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