I have a problem I need help with. I have the following Matrix A:

I need to find an elementary matrix with subtracts 2 times column 4 from column 2 of matrix A.

I have no idea where to start, and I can't find a good reference source.

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- Nov 9th 2009, 01:22 PMnotgodFinding Elementary Matrix
I have a problem I need help with. I have the following Matrix A:

I need to find an elementary matrix with subtracts 2 times column 4 from column 2 of matrix A.

I have no idea where to start, and I can't find a good reference source.

- Nov 9th 2009, 03:18 PMJameson
This is easier than it seems. Elementary matrices are just matrices that result from elementary matrix operations. For this problem, look at columns 4 and 2. Can you find ? I bet so. What about ? I bet so.

Now the new matrix will be the starting one with column 2 being changed to the answer from above. - Nov 10th 2009, 06:07 AMHallsofIvy
I think you are confusing terminology. An "elementary matrix" doesn't depend on a "matrix A". If you are looking for an elementary matrix that "subtracts 2 times column 4 from column 2" of any matrix it multiplies, just set up the 5 by 5 identity matrix and subtract two times column 4 from column 2 of it. That is, all except column 2 will be unchanged and it will just have a "-2" in the 4th row, in addition to the "1" in the second row.