How to change the variable by it's value in a numpy array

Question

I have this numpy array

a=np.array([[2*y, 0],[2*x + 1, 2*y + 4]])

I want to replace (x,y) by a value, for example (1,1).

How can I have this array with this new values in order to have something like this:

a=[[2,0],[3,6]]

Possible duplicate of stackoverflow.com/questions/34735193/… — yasouser
– yasouser, Commented Apr 13, 2017 at 20:27
How about creating a function, say make_array(x, y), that returns the array a? — Warren Weckesser
– Warren Weckesser, Commented Apr 13, 2017 at 20:28
If you are asking about modifying the array inplace, then see this question: stackoverflow.com/questions/10149416/… — yasouser
– yasouser, Commented Apr 13, 2017 at 20:30

MSeifert · Accepted Answer · 2017-04-13 20:58:59Z

1

You can use SymPy (a symbolic math package) and it's Matrix (array):

>>> from sympy import Matrix
>>> from sympy.abc import x, y
>>> m = Matrix([[2*y, 0],[2*x + 1, 2*y + 4]])
>>> m
Matrix([
[    2*y,       0],
[2*x + 1, 2*y + 4]])

>>> n = m.subs({x: 1, y: 1})   # replace variables with values
>>> n
Matrix([
[2, 0],
[3, 6]])

>>> np.array(n).astype(int)    # convert to numpy array
array([[2, 0],
       [3, 6]])

edited Apr 13, 2017 at 20:58

answered Apr 13, 2017 at 20:46

MSeifert

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