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Given a matrix A, you want to compute its determinant using LU decomposition. Which expression correctly computes det(A)?

hard📝 Application Q9 of 15
SciPy - Linear Algebra (scipy.linalg)
Given a matrix A, you want to compute its determinant using LU decomposition. Which expression correctly computes det(A)?
Adet(A) = product of diagonal elements of L times product of diagonal elements of U
Bdet(A) = det(P) * product of diagonal elements of U
Cdet(A) = sum of diagonal elements of U
Ddet(A) = det(L) + det(U)
Step-by-Step Solution
Solution:
  1. Step 1: Recall determinant properties in LU decomposition

    LU decomposition gives PA = LU, so det(P)*det(A) = det(L)*det(U).
  2. Step 2: Use determinant facts

    Since L is lower triangular with unit diagonal, det(L) = 1. So det(A) = det(P) * det(U), and det(U) is product of U's diagonal elements.
  3. Final Answer:

    det(A) = det(P) * product of diagonal elements of U -> Option B
  4. Quick Check:

    det(A) = det(P) * ∏ diag(U) [OK]
Quick Trick: Determinant = det(P) times product of U diagonal [OK]
Common Mistakes:
MISTAKES
  • Multiplying diagonal elements of L and U
  • Adding determinants instead of multiplying
  • Ignoring permutation matrix determinant

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