How do I find the determinant of a 2x2 matrix?

Question

It has to be ad-bc Here is my code but it says that a aList is not defined

def findDeterminate(alist):
    value=0
    aList = [[a,b],[c,d]]
    for i in range (0, len(aList)):
        value = aList[0][1]*aList[1][2] - aList[0][2]*aList[1][1]

def main():
    a = str(input("what is your first value"))
    b = str(input('what is your second value'))
    c = str(input('what is your third value'))
    d = str(input('what is your fourth value'))
    return findDeterminate(aList)

The `for` loop does nothing, get rid of it. The `findDeterminate()` function does not return a value. The `str()` function creates strings, you want `float()` instead. The `aList` assignment should be moved to `main()`. — Dietrich Epp, Oct 14 '14 at 17:27

score 1 · Answer 1 · answered Oct 14 '14 at 17:23

I won't solve this for you, but will give some hints:

There is no aList in main().
You've misspelt aList as alist in the definition of findDeterminate().
What's the purpose of the for loop?
A two-element list has no element at index 2.
You are not returning anything from findDeterminate().
main() has no special meaning in Python and is not called automatically.

(BTW, the determinant of a matrix is spelled "determinant" and not "determinate".)

score 0 · Answer 2 · answered Oct 20 '20 at 20:37

# Determinant of a 2x2 matrix
matrixG = [[2, 1],
           [3, 4]]

if len(matrixG) != 2 or len(matrixG[0]) != 2:
    print("Matrix should be 2x2 matrix only")
else:
    determinant = (matrixG[0][0] * matrixG[1][1]) - (matrixG[0][1] * matrixG[1][0])
    print(determinant)

How do I find the determinant of a 2x2 matrix?

2 Answers2