Deleting Row and Column

2020 4 24
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更新时间：2020 4 25
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I am doing a project with matrices. I want to change the size of the matrix by deleting the last 2 rows and the last 2 column. I want to go from 0.01 to 0.15 in steps of 0.01. When I display Q1 I am able to delete the last 2 columns but the the last 2 rows and then when I try to delete the rows (disp Q2) it deleted the rows but not the columns. I want BOTH the last two ROW AND last two COLUMN to be deleted from the Matrix P. Any help is appreciated!!!!
P = [0.1 0.75 0 0 0.15 0; 0 0.1 0.8 0 0.10 0; 0 0 0.15 0.75 0.1 0; 0 0 0 0.1 0.1 0.8; 0 0 0 0 1 0; 0 0 0 0 0 1];
disp(P)
for v = 0.01:0.01:0.15
P(1,1) = v + P(1,1);
%disp(P)
Q1 = ([:,1 2 3 4]);
disp(Q1)
Q2 = P([1 2 3 4],:);
%Q2 = P(:, [5 6]);
disp(P)
end

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回答（2 个）

KSSV
KSSV 2020-4-24

0 个投票

If A is your matrix, you can remove last two rows and columns using:
[m,n] = size(A) ;
A(m-1:m,:) = [] ; % removes last two rows
A(:,n-1:n) = [] ; % removes last two columns

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Imani DaSilva
Imani DaSilva 2020-4-24
when I try this method i am getting an error saying "Index in position 1 is invalid. Array indices must be positive integers or logical values." it prints out the first matrix correctly and then runs into that error.
KSSV
KSSV 2020-4-24
Show us the code which you have tried.

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James Tursa
James Tursa 2020-4-24

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Q = P(1:end-2,1:end-2);

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Imani DaSilva
Imani DaSilva 2020-4-24
This worked! Thank you. One final question, if i wanted to just get the last two colums of the matrix without the last 2 rows, how would I go about doing that?
Imani DaSilva
Imani DaSilva 2020-4-24
from what i understand P(1:end-2,1:end-2) is for the subtracting the last two rows and colums starting from column 1 and row 1. So if i wanted to get the last 2 columns without the last 2 rows. I tried the same concept with removing the last 2 rows but extracting the last 2 columns and it is just giving me a vector of 1's. But i would want
0.1500 0
0.1000 0
0.1000 0
0.1000 0.8000
(1.0000 0) ->minus this row
(0 1.0000) -> minus this row
Imani DaSilva
Imani DaSilva 2020-4-24
I figured it out! thanks for the help

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