Getting a numpy.ndarray object is not callable error

Question

Hey guys I'm receiving an error and I'm not 100% sure why it's happening. I'm trying to perform both the eulers and heun's methods and plot them against one another. Any help or suggestions would be awesome! I'm pretty novice with python so this is a bit new to me.

import numpy
#eulers 
yi = 0
h = 0.2
te = [0.0,2.0,0.2]
def euler(f, y0, t):
    n = len(t)
    y = numpy.array([y0] * n)
    for i in range(n - 1):
        y[i+1] = y[i] + (t[i+1] - t[i]) * f(y[i], t[i])
    return y
fy = (y*t**3) - 1.5*y
y1 = euler(fy, yi, te)

#heun
def heun(f, y0, t):
    n = len(t)
    y = numpy.array( [y0] * n )
    for i in range(n - 1):
        h = t[i+1] - t[i]
        k1 = h * f( y[i], t[i])
        k2 = h * f( y[i] + k1, t[i+1])
        y[i+1] = y[i] + (k1 + k2) / 2.0
    return y

y2 = heun(fy, 1, te)

tp = numpy.linspace(0.0, 2.0, 0.2)
plt.plot(tp, y1,'r-',linewidth=2,label='Eulers')
plt.plot(tp, y2,'b--',linewidth=2,label='Heun')
plt.xlabel('time')
plt.ylabel('y(t)')
plt.legend()
plt.show()

This is my error code:

TypeError                                 Traceback (most recent call last)
<ipython-input-152-395afeefc50a> in <module>()
     11     return y
     12 fy = (y*t**3) - 1.5*y
---> 13 y1 = euler(fy, yi, te)
     14 
     15 #heun

<ipython-input-152-395afeefc50a> in euler(f, y0, t)
      8     y = numpy.array([y0] * n)
      9     for i in range(n - 1):
---> 10         y[i+1] = y[i] + (t[i+1] - t[i]) * f(y[i], t[i])
     11     return y
     12 fy = (y*t**3) - 1.5*y

TypeError: 'numpy.ndarray' object is not callable

t is not defined... y is not defined... Where did you copy/paste this from? — Reblochon Masque
– Reblochon Masque, Commented Dec 1, 2017 at 4:39
If someone ran your code as you've shown, they would get a different error from you. It would fail on the line that defines fy because of the issues mentioned in the previous comment. It looks like you're using python interactively. Make sure when you post code that your code would run (or not run) as you expect in a brand new python session. — Gus
– Gus, Commented Dec 1, 2017 at 4:45

Gus · Accepted Answer · 2017-12-01 04:45:15Z

2

My guess is that you're trying to define a function f(y,t) in the line

fy = (y*t**3) - 1.5*y

as your differential equation. However, that is not how you define a function in python.

Try

def f(y,t): return y*t**3 - 1.5*y

You are getting an error because on line ---> 10 y[i+1] = y[i] + (t[i+1] - t[i]) * f(y[i], t[i])

f is a NumPy array, but you are treating it as a function.

answered Dec 1, 2017 at 4:45

Gus

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