Why does the SORTROWS function give incorrect results for complex matrices in MATLAB 7.2 (R2006a)?

I am trying to sort my complex matrix with respect to the second column using the SORTROWS function in MATLAB 7.2 as follows:

test=[0:.05:1;0:.05:1]';

test(19,1)=test(19,1)+.2i;

test(19,2)=-test(19,2);

a=sortrows(test,2);

plot(a(:,2))

As seen from the plot, the rows are sorted in incorrect order.

Answer 1

[MathWorks Support Team]

The documentation for the SORTROWS function mentions the following:

When A is complex, the elements are sorted by magnitude.

The above is true even if the column provided to the SORTROWS function is real. The SORTROWS function cannot be used to sort according to real behavior on a complex matrix.

You may instead, use SORT on the real column, then use the returned indices to manipulate the original matrix as follows:

test=[0:.05:1;0:.05:1]';

test(19,1)=test(19,1)+.2i;

test(19,2)=-test(19,2);

test2=test;

[a,b]=sort(test(:,2))

clear a;

for j = 1:length(test)

      test2(j,:) = test(b(j),:); 

end

clear test

plot(test2(:,2))