Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.soft-sys.math.mathematica > #1281

Re: LUDecomposition

Show all headers | View raw

Kevin wrote:
> LUDecomposition[{{1, 2}, {3, 4}}]
> and
> LUDecomposition[{{3, 4}, {1, 2}}]
> both give the same output:
> {{{1, 2}, {3, -2}}, {1, 2}, 1}
> 
> Only the output for the first matrix is correct.
> 
> Alpha gives the same incorrect results for the 2nd matrix
> correct 1st matrix: http://www.wolframalpha.com/input/?i=LUDecomposition+{{1%2C2}%2C{3%2C4}}
> incorrect 2nd matrix: http://www.wolframalpha.com/input/?i=LUDecomposition+{{3%2C4}%2C{1%2C2}}
> 

In versions I tried, I get for the second case

LUDecomposition[{{3, 4}, {1, 2}}]

Out[1]= {{{1, 2}, {3, -2}}, {2, 1}, 1}

This is correct.

I am not sure if Wolfram|Alpha is correct. Possibly it is failing to 
account for the permutation vector.

Daniel Lichtblau
Wolfram Research

Back to comp.soft-sys.math.mathematica | Previous | Next | Find similar | Unroll thread

Thread

Re: LUDecomposition Daniel Lichtblau <danl@wolfram.com> - 2011-03-30 09:15 +0000

csiph-web