ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
The above error is what I got for the below code intended to plot the piecewise function created. Can't figure it out.
import numpy as np
import matplotlib.pyplot as plt
def f(x):
if x>=0 and x<=1:
return x
elif x>1 and x<=2:
return 2-x
else:
return 0
xlist = np.linspace(0,1,num = 1000)
ylist = f(xlist)
plt.plot(ylist,xlist)
plt.show()
As per comments, you need to vectorize your method f (and also fix some mistakes):
import numpy as np
import matplotlib.pyplot as plt
def f(x):
y = np.empty_like(x)
mask1 = (0 <= x) & (x <= 1)
mask2 = (1 < x) & (x <= 2)
mask3 = np.logical_not((0 <= x) & (x <= 2)) #or ~((0 <= x) & (x <= 2))
y[mask1] = x[mask1]
y[mask2] = 2 - x[mask2]
y[mask3] = 0
return y
xlist = np.linspace(-1, 3, num = 1000)
ylist = f(xlist)
plt.plot(xlist, ylist)
plt.show()
You might also find that mask3 is not necessarry and vectorize a method f like this:
def f(x):
y = np.full_like(x, fill_value=0) #or np.zeros_like(x)
mask1 = (0 <= x) & (x <= 1)
mask2 = (1 < x) & (x <= 2)
y[mask1] = x[mask1]
y[mask2] = 2 - x[mask2]
return y
3 (and use y = np.zeros_like(x) instead). I've implemented it in a way that works in a more general way assuming OP would want to pad remaining values with anything else than zeros.What I understood is , you are basically comparing an array with a number which should not be the case here, the code provided might help you with solution,
import numpy as np
import matplotlib.pyplot as plt
def f(x):
if x>=0 and x<=1:
return x
elif x>1 and x<=2:
return 2-x
else:
return 0
xlist = np.linspace(0,1,num = 1000,endpoint=False)
ylist = np.array([f(num) for num in xlist])
plt.plot(xlist,ylist)
plt.show()
You can use the function you have already defined and vectorize is using np.vectorize.
import numpy as np
import matplotlib.pyplot as plt
def f(x):
if x>=0 and x<=1:
return x
elif x>1 and x<=2:
return 2-x
else:
return 0. # make this change to ensure float values
xlist = np.linspace(0,1,num = 1000)
ylist = np.vectorize(f)(xlist)
plt.plot(ylist,xlist)
plt.show()
The issue you are running into in your code is that you are passing an array to f rather than applying f element-wise, so any comparison gives an array of True or False values; this is what is ambiguous in the error message. Using np.vectorize will change the function defined to apply to each element of the array and give you the desired output.
