Construct a matrix using a for loop

Question

I have calculated 9 matrix elements named sij, with i and j being variables (i,j = [1, 2, 3]). Here, i denotes rows and j columns. Suppose I want a 3×3 matrix that consists of the matrix elements s11, s12, … s32, s33 (nine elements in total).

s11 = 1
s12 = 2
s13 = 3
(...)
s33 = 9

How can I use for loops to construct a matrix out of these elements? Like this:

matrix = [[s11, s12, s13], [s21, s22, s23], [s31, s32, s33]]

So that I get a matrix that looks like this.

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

Asked By: Retze

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Source

Answer 1

I would consider renaming the sij to s[i][j]. Then using them in loops would be trivial.

s[1][1] = 1
s[1][2] = 2
s[1][3] = 3
(...)
s[3][3] = 9

Then:

instead of:

matrix = [[s11, s12, s13], [s21, s22, s23], [s31, s32, s33]]

You can have the following two nested loops to construct the matrix.

for i in (1,4):
   for j in (1,4):

BTW, having a 0 based numbering would be more Pythonic.

Answered By: boardrider

Answer 2

You are better off writing an array and reshaping such that you don’t need to type out elements to variables but here is a one-liner

>> np.reshape([eval('s{0}{1}'.format(x,y)) for x in range(1,4) for y in range(1,4)], (3,3))
array([[1, 2, 3],
       [4, 5, 6],
       [7, 8, 9]]

Answered By: percusse

Answer 3

We can use this code for creating our desired matrix with for loop:

n = int(input('n:'))

for i in range(1,n):

    for j in range(1,n):

        if i<j:
            print(1,end = ' ')
        else :

            print('0',end = ' ')

    print()

Output

Answered By: Adolhamid Fazeli Eydini

Construct a matrix using a for loop

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