Talk:LU decomposition: Difference between revisions
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== Python example contains error == |
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The Python example has a divide by zero error for the matrix |
The Python example has a divide by zero error for the matrix |
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The permutation matrix has to be updated at each step, but that will make the code a lot more complicated. |
The permutation matrix has to be updated at each step, but that will make the code a lot more complicated. |
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== Example 2 pivot matrix seems to be wrong == |
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The pivot matrix in example 2 should also swap the last two rows of the current resulting pivoted matrix: A'(3, 3) = 2 while there is a 7 right beneath it. Here is the result of the multiplication of the two matrices on [http://www.wolframalpha.com/input/?i=matrix+multiplication+calculator&f1={{1%2C0%2C0%2C0}%2C{0%2C0%2C1%2C0}%2C{0%2C1%2C0%2C0}%2C{0%2C0%2C0%2C1}}&f=MatricesOperations.theMatrix1_{{1%2C0%2C0%2C0}%2C{0%2C0%2C1%2C0}%2C{0%2C1%2C0%2C0}%2C{0%2C0%2C0%2C1}}&f2={{11%2C9%2C24%2C2}%2C{1%2C5%2C2%2C6}%2C{3%2C17%2C18%2C1}%2C{2%2C5%2C7%2C1}}&f=MatricesOperations.theMatrix2_{{11%2C9%2C24%2C2}%2C{1%2C5%2C2%2C6}%2C{3%2C17%2C18%2C1}%2C{2%2C5%2C7%2C1}}&a=*FVarOpt.1-_**-.***MatricesOperations.theMatrix3---.*-- wolfram alpha] |
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The pivot matrix I propose is {{1,0,0,0},{0,0,1,0},{0,0,0,1},{0,1,0,0}}. |
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I did not change the article because it seemed very strange that I would be the first to see this and I therefore wonder if I'm not wrong. |
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Revision as of 13:57, 20 July 2015
Python example contains error
The Python example has a divide by zero error for the matrix
b = [[1, 1, 1, 1], [1, 1, -1, -1], [1, -1, 0, 0], [0, 0, 1, -1]]
although a LUP decomposition exists: [1]
The permutation matrix has to be updated at each step, but that will make the code a lot more complicated.
Example 2 pivot matrix seems to be wrong
The pivot matrix in example 2 should also swap the last two rows of the current resulting pivoted matrix: A'(3, 3) = 2 while there is a 7 right beneath it. Here is the result of the multiplication of the two matrices on wolfram alpha
The pivot matrix I propose is {{1,0,0,0},{0,0,1,0},{0,0,0,1},{0,1,0,0}}.
I did not change the article because it seemed very strange that I would be the first to see this and I therefore wonder if I'm not wrong.