Creat a matrix based off an if statement

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Jonathan Ish-Shalom 2020-4-23

0
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关闭： MATLAB Answer Bot 2021-8-20

I am trying to make a look and when IFIX(J,K) == 0 I want the certain column from Global_K to populate displacement. However, each time i run the if statement it rewrites over the same column. I want it to add a new column each time. Please help!

        if IFIX(J,K) == 0
            for L = 1:(NJ*NDJ)
        displacement(L) = Global_K(L,NRC);
                end
            end
        else
            for L = 1:(NJ*NDJ)
        Global_K(L,NRC) = 0;
            
            end
        end

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Darren Wethington 2020-4-23

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Currently, displacement will only ever be a vector of length NJ*NDJ. If you want multiple columns, you have to add them. A tip: to add a column to an existing matrix, perform the following:

matrix = [];
vector = 1:10;
matrix = [matrix; vector];
matrix = [matrix; vector];
disp(matrix);

Adjust that so it does what you want (this concatenates a row vector to the bottom of the matrix).

Jonathan Ish-Shalom 2020-4-23

编辑：Jonathan Ish-Shalom 2020-4-23

No this didn't do what I wanted to do.

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Answer 1

Raunak Gupta 2020-4-28

1
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Hi,

From the functionality of the code I see a better way to write the code. Here I see array indexing can be used to avoid lot of for loops. Hope the below code achieves what is required.

% For experiment assuming values of NJ and NDJ
NJ = 5;
NDJ = 4;
Global_K = randi([1 100],[NJ*NDJ,NJ*NDJ]);
IFIX = randi([0 2],[NJ,NDJ]);
% Actual Logic
condition = IFIX==0;
% For flattening the matrix to get row-wise NRC
conditionTranspose = condition.';
% Final Indices of Global_K to add to displacement
conditionFinal = conditionTranspose(:);
displacement = Global_K(:,conditionFinal);
Global_K(:,conditionFinal) = 0;