how to delete certain columns and rows from matrix

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Antrea Plastira
Antrea Plastira 2022-10-5
评论： William Rose 2022-10-5
I have the matrix
M = [1000 -1000 0 0;
-1000 10000 0 -9000;
0 0 5000 -5000;
0 -9000 -5000 14000];
and I want to get the matrix when the 1st column and row and the 3rd column and row are gone, so that Mnew = [10000 -9000;
-9000 14000];
Any help?

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采纳的回答

William Rose
William Rose 2022-10-5
Ran in:
@Antrea Plastira,
M = [1000 -1000 0 0;
-1000 10000 0 -9000;
0 0 5000 -5000;
0 -9000 -5000 14000];
Mnew=M([2,4],[2,4])
Mnew = 2×2
10000 -9000 -9000 14000
The line above keeps specifies the rows and columns to keep.

更多回答（2 个）

Steven Lord
Steven Lord 2022-10-5
Ran in:
Do you know which rows/columns you want to delete or which ones you want to keep? If to keep:
M = magic(4)
M = 4×4
16 2 3 13 5 11 10 8 9 7 6 12 4 14 15 1
toKeep = [2 4];
A = M(toKeep, toKeep)
A = 2×2
11 8 14 1
If to delete:
M = magic(4)
M = 4×4
16 2 3 13 5 11 10 8 9 7 6 12 4 14 15 1
toDelete = [1 3];
M(toDelete, :) = []
M = 2×4
5 11 10 8 4 14 15 1
M(:, toDelete) = []
M = 2×2
11 8 14 1
William Rose
William Rose 2022-10-5
Ran in:
If you want to sepcify the rows and columns to delete:
M = [1000 -1000 0 0;
-1000 10000 0 -9000;
0 0 5000 -5000;
0 -9000 -5000 14000];
Mnew=M;
rows2delete=[1,3];
cols2delete=rows2delete;
Mnew(rows2delete,:)=[];
Mnew(:,cols2delete)=[]
Mnew = 2×2
10000 -9000 -9000 14000
Try it.

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