Get the magnitude of a vector (x,y)

Question

I’m struggling to get this to work because all the answers I can find that most answers are more focused on vectors in numpy arrays and not like mine in classes (OOP). (I hope I am phrasing all this the correct way, please excuse if I am not).

I want to find the magnitude of a vector (x,y), here is my code:

class Vector(object):

    def __init__(self, x, y):
        self.x = x
        self.y = y

I have code that can sum and subtract the two vectors, but how to get the magnitude with this equation:

magnitude = math.sqrt(sum(v**2 for v in vector))

This is my code but it is not giving me what I need:

def vector_mag(self):
        x_vector = self.x
        y_vector = self.y
        vector = (x_vector, y_vector)
        magnitude = math.sqrt(sum(v**2 for v in vector))
        return Vector(magnitude)

This gives an error that says:

line 22, in

print vector.vector_mag()

line 14, in vector_mag

return Vector(magnitude)

TypeError: init() takes exactly 3 arguments (2 given)

So when I add another "string" in the return part like this…:

return Vector("Vector magnitude is:", magnitude)

…the program runs but gives a strange result.

What am I doing wrong?

Here is my "full" code:

import math

class Vector(object):

  def __init__(self, x, y):
       self.x = x
       self.y = y

  def vector_mag(self):
       x_vector = self.x
       y_vector = self.y
       vector = (x_vector, y_vector)
       magnitude = math.sqrt(sum(v**2 for v in vector))
       return Vector("Vector magnitude is: ", magnitude)

vector1 = Vector(10, 1)

vector2 = Vector(20, 2)

vector_list = [(vector1), (vector2)]

for vector in vector_list:

 print vector.vector_mag()

Asked By: Lee

||

Source

Answer 1

return Vector(magnitude)

The magnitude of a vector is a scalar value; in other words, it’s a single number. A vector is a collection of numbers, so it doesn’t make sense to try to convert a scalar to a vector. Just return the magnitude unchanged.

return magnitude

Answered By: Kevin

Answer 2

You can define vector_mag like so:

def __abs__(self):
    return (self.x ** 2 + self.y ** 2) ** 0.5

Then calling your method is as easy as this:

vector1 = Vector(10, 1)
print 'Magnitude =', abs(vector1)

Answered By: Noctis Skytower

Answer 3

For accuracy reason, you should use math hypot to avoid any overflow.

from math import hypot

def __abs__(self):
    return hypot(self.x, self.y)

math.hypot(x, y): Return the Euclidean norm, sqrt(x*x + y*y). This is the length of the vector from the origin to point (x, y).

This would give:

from math import hypot
class Vector(object):

    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __abs__(self):
        return hypot(self.x, self.y)

v=Vector(3,1)
magnitude = abs(v)

Answered By: Guillaume Jacquenot

Get the magnitude of a vector (x,y)

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