logic in matlab to filter result

Question

ali hassan 2020-11-18

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https://ww2.mathworks.cn/matlabcentral/answers/652378-logic-in-matlab-to-filter-result

编辑： Image Analyst 2020-11-19

HELLO everyone.

i have a little query,.plzz answer in brief for better understanding.

actually i am getting the following two solutions as mentioned in each column as x,y and z.now i want to only keep the column in which value of z(bottom value) is positive.

plzz correct the code and mention it in comments.

CODE:

idx = any(possibleSol < 0) | any(imag(possibleSol) ~=0);

possibleSol(:, idx) = [ ];

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Answer 1

Image Analyst 2020-11-18

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在 MATLAB Online 中打开

Try this

% Extract z from the last row of possibleSol.
z = possibleSol(3, :);
% Find out which columns have the last row (z) as positive.
goodColumns = z > 0;
% Extract only those columns where z > 0
possibleSol = possibleSol(:, goodColumns)

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Image Analyst 2020-11-18

编辑：Image Analyst 2020-11-19

在 MATLAB Online 中打开

You can read : as basically "all rows". And idx is just a bad name for the variable -- it should be called goodIndexes or something much more descriptive than idx. Don't you just hate it when people use confusing, cryptic variable names? Anyway idx is a logical vector that says, for each element, whether to extract that column or not. For example

m = m(:, [1,1,0,0,1]);

would say to take all rows of m, but only columns 1, 2, and 5 and put those 3 extracted columns back into m.

Conversely, if I said

m(:, [1,1,0,0,1]) = [];

it says to remove columns 1, 2, and 5 by setting them equal to "null", or "empty", which is indicated by the two square brackets with nothing inside. So after that matrix m would contain only columns 3 and 4.

ali hassan 2020-11-19