MATLAB: “For improved robustness, consider replacing i and j by 1i” – Is this an error

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I would like to know if the red line is an error. It says that: "For improved robustness, consider replacing i and j by 1i". I need to replace or I can just leave it as it is? Thanks

Best Answer

Matlab uses i and j for imaginary i, or sqrt(-1). This lead to a lot of issues because i and j are often used as counter variables for the for and while loops. Example:

for i = 1:10
    plot(ano3, medial5(i-7), 'k');  %Did you mean imaginary i or counter variable i? 
end

In your case, it depends on if i is the imaginary i or a variable i. If imaginary i, take their advice and use 1i, or you may end up spending hours looking for the i bug. If variable i, you must declare i before hand, or it'll assume i = 1i.

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Theory one: You use i as a variable. As this is a "reserved word" for complex calculations, there may be an unexpected effect.

Theory two: One of your functions or variables shadows the real MATLAB command and does something unexpected. Like you would assign plot=1 the then try to use the plot command.

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xy - it seems as if your code is iterating over the y array and looking for those elements which are a maximum with respect to its neighbours

 if (y(i-1)<y(i) && y(i+1)<y(i))

When this is true, what do you want to save: that maximum value or its index into y? If the former, then you should be saving y(i) and if the latter, then you should be saving i. Something like

 maximumValues = [maximumValues y(i)];  % (1)

 maximumIdcs = [maximumIdcs ; i]        % (2)

where we have initialized either array to the empty matrix (like you have done for maxim). Either of the above would replace your code

 for j=1:(j+1)
    maxim(j) = y(i)
 end

which I don't quite follow. The above iterates from 1 to j+1, replacing the first j+1 elements of maxim with the same y(i). This is why your maxim array has identical values...because they are getting reset (or initialized) to same y(i). I think that you just need to replace this with (1) or (2) from above and you will be have what you are looking for.

As an aside, it is better to not use i and j as indexing variables as MATLAB uses both of these to represent the imaginary number.

Best Answer

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