Suppose A is an n x n invertible unit lower triangular matrix and n » 10. A programmer claims that as solving a linear system Ax = b takes around 10 seconds, solving ten linear systems Ax; = b; for j = 1, ..., 10 will take around 100 seconds. Justify or refute this claim. FALSE. Just need to compute the LU factorization of the matrix A once, then use forward and back substitutions to solve LUx; = Pb, for j = 1, ..., 10. This will not take much more than 10 seconds. TRUE. It takes 10 times longer to compute the solution of 10 linear systems using just forward or back substitution.

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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Suppose A is an n x n invertible unit lower triangular matrix and n > 10. A programmer claims that as solving a linear system
Aæ = b takes around 10 seconds, solving ten linear systems Aæ; = b; for j = 1, ..., 10 will take around 100 seconds.
Justify or refute this claim.
FALSE. Just need to compute the LU factorization of the matrix A once, then use forward and
back substitutions to solve LUæ; = Pb; for j = 1, ..., 10. This will not take much more than
10 seconds.
TRUE. It takes 10 times longer to compute the solution of 10 linear systems using just forward or
back substitution.
Transcribed Image Text:Suppose A is an n x n invertible unit lower triangular matrix and n > 10. A programmer claims that as solving a linear system Aæ = b takes around 10 seconds, solving ten linear systems Aæ; = b; for j = 1, ..., 10 will take around 100 seconds. Justify or refute this claim. FALSE. Just need to compute the LU factorization of the matrix A once, then use forward and back substitutions to solve LUæ; = Pb; for j = 1, ..., 10. This will not take much more than 10 seconds. TRUE. It takes 10 times longer to compute the solution of 10 linear systems using just forward or back substitution.
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