How to set axis ticks in multiples of pi (Python) (matplotlib)

Question

I'd like to make a plot in Python and have x range display ticks in multiples of pi.

Is there a good way to do this, not manually?

I'm thinking of using matplotlib, but other options are fine.

EDIT 3: EL_DON's solution worked for me like this:

import matplotlib.ticker as tck import matplotlib.pyplot as plt import numpy as np  f,ax=plt.subplots(figsize=(20,10)) x=np.linspace(-10*np.pi, 10*np.pi,1000) y=np.sin(x)  ax.plot(x/np.pi,y)  ax.xaxis.set_major_formatter(tck.FormatStrFormatter('%g $\pi$')) ax.xaxis.set_major_locator(tck.MultipleLocator(base=1.0))  plt.style.use("ggplot")   plt.show() 

giving:

EDIT 2 (solved in EDIT 3!): EL_DON's answer doesn't seem to work right for me:

import matplotlib.ticker as tck import matplotlib.pyplot as plt import numpy as np  f,ax=plt.subplots(figsize=(20,10)) x=np.linspace(-10*np.pi, 10*np.pi) y=np.sin(x)  ax.plot(x/np.pi,y)  ax.xaxis.set_major_formatter(tck.FormatStrFormatter('%g $\pi$')) ax.xaxis.set_major_locator(tck.MultipleLocator(base=1.0))  plt.style.use("ggplot")  plt.show() 

gives me

which really doesn't look right

Answer 1

This is inspired by Python Data Science Handbook, although Sage attempts to do without explicit parameters.

EDIT: I've generalized this to allow you to supply as optional parameters the denominator, the value of the unit, and the LaTeX label for the unit. A class definition is included if you find that helpful.

import numpy as np import matplotlib.pyplot as plt  def multiple_formatter(denominator=2, number=np.pi, latex='\pi'):     def gcd(a, b):         while b:             a, b = b, a%b         return a     def _multiple_formatter(x, pos):         den = denominator         num = np.int(np.rint(den*x/number))         com = gcd(num,den)         (num,den) = (int(num/com),int(den/com))         if den==1:             if num==0:                 return r'$0$'             if num==1:                 return r'$%s$'%latex             elif num==-1:                 return r'$-%s$'%latex             else:                 return r'$%s%s$'%(num,latex)         else:             if num==1:                 return r'$\frac{%s}{%s}$'%(latex,den)             elif num==-1:                 return r'$\frac{-%s}{%s}$'%(latex,den)             else:                 return r'$\frac{%s%s}{%s}$'%(num,latex,den)     return _multiple_formatter ​ class Multiple:     def __init__(self, denominator=2, number=np.pi, latex='\pi'):         self.denominator = denominator         self.number = number         self.latex = latex ​     def locator(self):         return plt.MultipleLocator(self.number / self.denominator) ​     def formatter(self):         return plt.FuncFormatter(multiple_formatter(self.denominator, self.number, self.latex)) 

This can be used very simply, without any parameters:

x = np.linspace(-np.pi, 3*np.pi,500) plt.plot(x, np.cos(x)) plt.title(r'Multiples of $\pi$') ax = plt.gca() ax.grid(True) ax.set_aspect(1.0) ax.axhline(0, color='black', lw=2) ax.axvline(0, color='black', lw=2) ax.xaxis.set_major_locator(plt.MultipleLocator(np.pi / 2)) ax.xaxis.set_minor_locator(plt.MultipleLocator(np.pi / 12)) ax.xaxis.set_major_formatter(plt.FuncFormatter(multiple_formatter())) plt.show() 

Or it can be used in a more sophisticated way:

tau = np.pi*2 den = 60 major = Multiple(den, tau, r'\tau') minor = Multiple(den*4, tau, r'\tau') x = np.linspace(-tau/60, tau*8/60,500) plt.plot(x, np.exp(-x)*np.cos(60*x)) plt.title(r'Multiples of $\tau$') ax = plt.gca() ax.grid(True) ax.axhline(0, color='black', lw=2) ax.axvline(0, color='black', lw=2) ax.xaxis.set_major_locator(major.locator()) ax.xaxis.set_minor_locator(minor.locator()) ax.xaxis.set_major_formatter(major.formatter()) plt.show() 

Answer 2

f,ax=plt.subplots(1) x=linspace(0,3*pi,1001) y=sin(x) ax.plot(x/pi,y) ax.xaxis.set_major_formatter(FormatStrFormatter('%g $\pi$')) ax.xaxis.set_major_locator(matplotlib.ticker.MultipleLocator(base=1.0)) 

I used info from these answers:

• https://stackoverflow.com/a/19972993/6605826
• https://stackoverflow.com/a/29188910/6605826