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[ Plot Piecewise Function in Python ]
I would like to plot the following piecewise function in Python using Matplotlib, from 0 to 5.
f(x) = 1, x != 2; f(x) = 0, x = 2
In Python...
def f(x):
if(x == 2): return 0
else: return 1
Using NumPy I create an array
x = np.arange(0., 5., 0.2)
array([ 0. , 0.2, 0.4, 0.6, 0.8, 1. , 1.2, 1.4, 1.6, 1.8, 2. ,
2.2, 2.4, 2.6, 2.8, 3. , 3.2, 3.4, 3.6, 3.8, 4. , 4.2,
4.4, 4.6, 4.8])
I have tried things like...
import matplotlib.pyplot as plt
plt.plot(x,f(x))
Or...
vecfunc = np.vectorize(f)
result = vecfunc(t)
Or...
def piecewise(x):
if x == 2: return 0
else: return 1
import matplotlib.pyplot as plt
x = np.arange(0., 5., 0.2)
plt.plot(x, map(piecewise, x))
ValueError: x and y must have same first dimension
But I am not using these functions correctly, and am now just randomly guessing how to do this.
Some answers are starting to get there... But the points are being connected into a line on the plot. How do we just plot the points?
Answer 1
The problem is that the function f
does not take an array as input but a single numer. You can:
plt.plot(x, map(f, x))
The map
function takes a function f
, an array x
and returns another array where the function f
is applied to each element of the array.
Answer 2
You can use np.piecewise on the array:
x = np.arange(0., 5., 0.2)
import matplotlib.pyplot as plt
plt.plot(x, np.piecewise(x, [x == 2, x != 2], [0, 1]))