calculation with if else statement

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kim chan
kim chan 2020-4-4
回答： Image Analyst 2020-4-4
Hello,
I have a problem about using if-else statement for the following calculation (given that the size of A is 100*60*1200, 100 and 60 indicate the long and lat; median_A, min_A and max_A also have the same size, i.e.100*60*1200):
anomaly=(median_A - A)/(median_A - min_A)*100 if A ≤ median_A
anomaly=(median_A - A)/(max_A - median_A)*100 if A > median_A
I wrote the following simple code but the result looks unrealistic (go beyond the range e.g. larger than 100) because the answer should be ranged between -100 and 100 (I also tried replacing = with ==, it still does not work):
if A <= median_A
anomaly = ((median_A - A)./(median_A - min_A)*100);
else
anomaly = ((median_A - A)./(max_A - median_A)*100);
end
Do any professionals know how to solve this problem? Many appreciations!

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采纳的回答

Image Analyst
Image Analyst 2020-4-4
You need to create a logical index (a "map") first of where A is less than its median. Then use that logical index to make the assignment
A = rand(10, 60, 1200); % Create sample data.
median_A = median(A(:))
max_A = max(A(:))
min_A = min(A(:))
% Find where A is less than it's median.
logicalIndexes = A <= median_A; % A 3-D logical array.
% First initialize everything:
anomaly = ((median_A - A)./(max_A - median_A)*100);
% Make up second set of numbers.
A2 = ((median_A - A)./(median_A - min_A)*100);
% Then replace only those indexes where A(i,j,k) < median_A
anomaly(logicalIndexes) = A2(logicalIndexes);
Also, look up the mad() and isoutier() functions.

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