38 lines
1.0 KiB
Python
38 lines
1.0 KiB
Python
from typing import List
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import determinate2x2
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import copy
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def neg_odd_vals(lst: List[int])-> List[int]:
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return [-val if i % 2 == 1 else val for i, val in enumerate(lst)]
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def det3x3(M: List[List[int]])->int:
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assert len(M) == 3 and len(M[0]) == 3, "Matrix is not 3x3"
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# Matrix M with row 0 and col 0 removed
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N = copy.deepcopy(M)
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N[1].remove(N[1][0])
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N[2].remove(N[2][0])
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A = [N[1], N[2]]
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#Matrix M with row 0 and col 1 removed
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N = copy.deepcopy(M)
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N[1].remove(N[1][1])
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N[2].remove(N[2][1])
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B = [N[1], N[2]]
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#Matrix M with row 0 and col 2 removed
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N = copy.deepcopy(M)
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N[1].remove(N[1][2])
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N[2].remove(N[2][2])
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C = [N[1], N[2]]
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# List M[0] with every odd index value set to its negative
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N0 = neg_odd_vals(N[0])
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# Sum of determinates A, B, C times their respective multipliers
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det0 = N0[0]*determinate2x2.det2x2(A)
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det1 = N0[1]*determinate2x2.det2x2(B)
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det2 = N0[2]*determinate2x2.det2x2(C)
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return det0 + det1 + det2
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