Use forLoop to manipulate values of elements in a specific column

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JZ
JZ 2015-12-5
评论： lsutiger1 2015-12-6
I created the following 5x5 matrix with no data:
mat = zeros(5:5)
mat =
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
I would like to use a for loop to generate the following result
mat =
0 0 0 0 0
0 0 0 10 0
0 0 0 20 0
0 0 0 30 0
0 0 0 40 0
I attempted using the following code, but the operation was performed on the first column - not the 4th, as I had intended.
for i = 2:length(mat(:,4))
mat(i) = mat(i-1) + 10;
end
This was the actual result
mat =
0 0 0 0 0
10 0 0 0 0
20 0 0 0 0
30 0 0 0 0
40 0 0 0 0
I imagine this is a simple syntax problem, but I am not finding the solution in any of the forums. Any help is appreciated.
Thanks

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采纳的回答

Star Strider
Star Strider 2015-12-5
This works:
mat = zeros(5:5);
mat(:,4) = 0:10:10*(size(mat,1)-1);
mat =
0 0 0 0 0
0 0 0 10 0
0 0 0 20 0
0 0 0 30 0
0 0 0 40 0
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JZ
JZ 2015-12-5
编辑：JZ 2015-12-5
That is indeed a much simpler solution - thank you!
And thanks for the clarification on cell/element. No offense taken.

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更多回答（1 个）

lsutiger1
lsutiger1 2015-12-5
You have only specified the row that you want to manipulate; you need to specify both the row and column.
mat(i) = mat(i-1,4) + 10;
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JZ
JZ 2015-12-5
Thanks, but I am still getting errors with both of your suggestions:
mat = zeros(5:5)
mat =
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
0 0 0 0 0
mat(i,4) = mat(i-4,4) + 10;
Index exceeds matrix dimensions.
mat(i) = mat(i-1,4) + 10;
Index exceeds matrix dimensions.
Suggestions?

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