CODEWITHSUNDEEP
python-3.xnumpynumerical-integration
Marco
Marco

Reputation: 81

calculate the absolute area from a graph that also gets negative

I want to calculate the absolute area under the given graph. What now happens is that it just integrates the line f. This line also gets negative. I am integrating from -5 to 5.

How can I adjust the function so it will give the absolute value?

edit: Something else I would like to know is how to calculate the area only where f(x) >0? Is there an option to do a double integral easily?

from numpy import *
import matplotlib.pyplot as plt

x = arange(-5,5.001,0.00001)
f = cos(4*x+1)**2 *(6 - 0.5* x**2)

print(trapz(f,x))
plt.plot([-5,5],[0,0])
plt.plot(x,f)
plt.show()

Upvotes: 1

Views: 1143

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476659

You can use numpy.abs(..) [numpy-doc] to calculate the element-wise absolute value for the array of values.

So we can calculate the values for f with:

f_abs = np.abs(f)
print(trapz(f_abs,x))

This will then calculate an approximation of the area, and thus consider the area under the x-axis to be positive as well.

If you want to ignore the negative parts, you can set negative values to 0 with numpy.clip(..) [numpy-doc]:

print(trapz(f.clip(min=0),x))

Upvotes: 1

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