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You have a matrix A and want to solve Ax = b using LU decomposition. Which step correctly describes how to find x?

hard📝 Application Q8 of 15
SciPy - Linear Algebra (scipy.linalg)
You have a matrix A and want to solve Ax = b using LU decomposition. Which step correctly describes how to find x?
ADecompose A into P, L, U; solve Lx = Pb; then solve Uy = x
BDecompose A into L, U; solve Ux = b; then solve Ly = x
CDecompose A into P, L, U; solve Ux = Pb; then solve Ly = x
DDecompose A into P, L, U; solve Ly = Pb; then solve Ux = y
Step-by-Step Solution
Solution:
  1. Step 1: Understand LU decomposition for solving Ax = b

    LU decomposition gives P, L, U such that PA = LU. To solve Ax = b, rewrite as LUx = Pb.
  2. Step 2: Solve system in two steps

    First solve Ly = Pb for y, then solve Ux = y for x.
  3. Final Answer:

    Decompose A into P, L, U; solve Ly = Pb; then solve Ux = y -> Option D
  4. Quick Check:

    Solving Ax=b via LU: Ly=Pb, then Ux=y [OK]
Quick Trick: Solve Ly=Pb first, then Ux=y to find x [OK]
Common Mistakes:
MISTAKES
  • Ignoring permutation matrix P in Pb
  • Solving equations in wrong order
  • Confusing variables y and x

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