How to plot arbitrary math functions using Python and matplotlib?

Question

I want to plot any mathematical function such as y=x**2 or y=sin(x)/x (anything basically). The problem is, I can only plot functions defined in numpy such as np.sin, np.cos or np.tan. The entire point here is how to avoid "hard coding" vectors and then plot those.

How can I plot arbitrary functions? Here is what I have so far:

import matplotlib.pyplot as plt
import numpy as np

#Let a be starting point on x
#Let b be end point on x
#Let f be the function you wish to plot

CornflowerBlue="6495ed"

def plotf(a,b,f):
    
    x=np.linspace(a,b,num=b*10)
    y=np.array([])
    
    for i in range (len(x)):
       
        y = np.append(y,f(x[i]))
        
    plt.grid(True)
    plt.plot(x,y,color="CornflowerBlue")
    plt.axhline(y=0,color="black")
    return

I can only plot functions defined in numpy such as np.sin, np.cos or np.tan. What do you mean by that? If i use plotf(-5, 5, lambda x: x**2 + 1) and then plt.show() it correctly renders a function that is not defined in numpy. — Countour-Integral
– Countour-Integral, Commented Dec 20, 2020 at 23:19
def f(x): return x**2 + 1 with plt.show() and plotf(-5, 5, f) works the same, I still don't get what your question is. — Countour-Integral
– Countour-Integral, Commented Dec 20, 2020 at 23:49
just a tip: if you're using numpy arrays, you don't need to loop through them. In other words, y = x**2 + 1 is all you need to do — Paul H
– Paul H, Commented Dec 21, 2020 at 0:02

Davide Fiocco · Accepted Answer · 2020-12-20 23:42:04Z

1

You could try sympy as it should allow you to play with a variety of mathematical functions without explicitly hardcoding them:

from sympy import *

def plotf(a,b,f):
    plot(f, xlim = (a,b)) 

plotf(-10, 10, "sin(x)/x") # or plotf(0, 2, "x**2"), or (almost) whatever

See for details https://docs.sympy.org/latest/modules/plotting.html!

edited Dec 20, 2020 at 23:42

answered Dec 20, 2020 at 23:22

Davide Fiocco

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