I am trying to plot a simple function in python ( x + sqrt(x^2 + 2x) ). Here is my code:
import pylab as pl
import numpy as np
import math
X = np.linspace(-999999,999999)
Y = (X+math.sqrt(X**2+2*X))
pl.plot(X,Y)
pl.show()
Here is the error that I am facing: TypeError: only length -1 arrays can be converted to Python scalars
use
Y = [(x+math.sqrt(x**2+2*x)) for x in X]
or
Y = map(lambda x: (x+math.sqrt(x**2+2*x)), X)
to generate a list of y-values.
You can also vectorize your function and apply it. See List comprehension, map, and numpy.vectorize performance for additional remarks.
Y = X+np.sqrt(X**2+2*X) ?The problem with your approach is that the math.sqrt function expects a single number as an input. Since you have a numpy-array with more than one element you should use the built-in numpy function sqrt as suggested by Rory Yorke i.e.
Y = X+np.sqrt(X**2+2*X
Since the numpy function is much more optimized it gives you a better performance, for example:
X = np.arange(10000)
timeit Y = map(lambda x: (x+math.sqrt(x**2+2*x)), X)
10 loops, best of 3: 82.1 ms per loop
timeit Y = X+np.sqrt(X**2+2*X)
10000 loops, best of 3: 108 µs per loop
