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Fixed determinant_fast() #3

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Fixed determinant_fast() #3

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c82370a
Fixed `determinant_fast()`
RandomGamingDev Nov 24, 2023
7cab1c8
Update LinearAlgebraPurePython.py
RandomGamingDev Nov 24, 2023
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18 changes: 15 additions & 3 deletions LinearAlgebraPurePython.py
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Original file line number Diff line number Diff line change
Expand Up @@ -326,9 +326,20 @@ def determinant_fast(A):
AM = copy_matrix(A)

# Section 2: Row manipulate A into an upper triangle matrix
odd_swaps = False
for fd in range(n): # fd stands for focus diagonal
if AM[fd][fd] == 0:
AM[fd][fd] = 1.0e-18 # Cheating by adding zero + ~zero
if AM[fd][fd] == 0: # Do a row swap with a row that won't result in a pivot of 0
found = False
for i in range(fd+1,n):
if AM[i][fd] != 0:
temp = AM[fd]
AM[fd] = AM[i]
AM[i] = temp
found = True
odd_swaps = not odd_swaps
break
if not found:
return 0 # If there are no other rows that can do that then return the determinant of 0
for i in range(fd+1, n): # skip row with fd in it.
crScaler = AM[i][fd] / AM[fd][fd] # cr stands for "current row".
for j in range(n): # cr - crScaler * fdRow, one element at a time.
Expand All @@ -338,7 +349,8 @@ def determinant_fast(A):
product = 1.0
for i in range(n):
product *= AM[i][i] # ... product of diagonals is determinant

if odd_swaps:
product *= -1
return product


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