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arraysmatrixnumpypython-2.7
Max Mines
Max Mines

Reputation: 43

Values of Variables Matrix NumPy

I'm working on a program that determines if lines intersect. I'm using matrices to do this. I understand all the math concepts, but I'm new to Python and NumPy.

I want to add my slope variables and yint variables to a new matrix. They are all floats. I can't seem to figure out the correct format for entering them. Here's an example:

import numpy as np

x = 2
y = 5
w = 9
z = 12

I understand that if I were to just be entering the raw numbers, it would look something like this:

matr = np.matrix('2 5; 9 12')

My goal, though, is to enter the variable names instead of the ints.

Upvotes: 4

Views: 17684

Answers (2)

Bi Rico
Bi Rico

Reputation: 25833

You can do:

M = np.matrix([[x, y], [w, z]])

# or
A = np.array([[x, y], [w, z]])

I included the array as well because I would suggest using arrays instead of of matrices. Though matrices seem like a good idea at first (or at least they did for me), imo you'll avoid a lot of headache by using arrays. Here's a comparison of the two that will help you decide which is right for you.

The only disadvantage of arrays that I can think of is that matrix multiply operations are not as pretty:

# With an array the matrix multiply like this
matrix_product = array.dot(vector)

# With a matrix it look like this
matrix_product = matrix * vector

Upvotes: 4

jackcogdill
jackcogdill

Reputation: 5122

Can you just format the string like this?:

import numpy as np

x = 2
y = 5
w = 9
z = 12

matr = np.matrix('%s %s; %s %s' % (x, y, w, z))

Upvotes: 2

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