Problem in sorting the elements of a complex column vetor in descending order.

Question

奥刘 2021-11-15

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1587069-problem-in-sorting-the-elements-of-a-complex-column-vetor-in-descending-order

评论：奥刘 2021-11-16

采纳的回答： Cris LaPierre

I am trying to sort the elements of a complex column vetor in descending order. The vector V is,

0.00192283028876372 + 2.81043109217511e-19i

0.00190176141109370 + 2.84699448762080e-19i

0.00147928037481547 - 2.74849838261212e-20i

0.00142769822781175 + 5.39004850343165e-20i

0.00117784972186107 + 2.08922253853130e-19i

0.00107796253204560 - 4.70645642035523e-20i

0.000800293022988111 + 1.22052572461947e-20i

0.000269899528923458 - 6.15654463989809e-20i

6.30592283269993e-05 - 7.50552502780072e-20i

2.23684164933882e-05 + 4.04939694038624e-21i

2.20073577954736e-05 - 5.80181618012595e-21i

1.95849840201760e-05 + 1.48445834874224e-20i

1.71925856406516e-05 - 1.15719050036467e-20i

1.28038961421133e-05 + 7.36148671834500e-20i

8.73059513582096e-06 + 1.23064435626381e-20i

6.28618594970652e-06 - 5.04267327744353e-20i

6.99991469893008e-08 - 1.02450891500650e-20i

2.80343931756963e-08 + 1.23048032017686e-20i

4.29713831923512e-09 + 3.73908633968205e-21i

2.28802604174547e-09 + 1.73500648980058e-20i

3.50507467296844e-10 - 1.10159115820306e-21i

7.32973689738923e-11 - 4.65099992985255e-21i

2.07808170074765e-11 - 2.84966374048803e-22i

4.68510672896002e-12 - 2.29503200085301e-21i

2.99051403313190e-12 + 3.62505072381834e-21i

1.32399364803625e-12 - 4.30261778360293e-21i

6.07212915777181e-13 + 2.79063028387683e-22i

1.23086553364893e-13 + 8.26560004261648e-21i

1.72392520759381e-14 + 1.86019192086409e-21i

1.01989680354965e-14 + 3.46136359467220e-21i

-8.05918955245067e-21 + 8.23317408693105e-22i

1.36822909718840e-15 - 1.33221528989010e-21i

I code as below,

% sort the variances in decreasing order

[junk, rindices] = sort(-1*V);

% V1=[2;6;4;3;1;8];

% [junk1, rindices1] = sort(-1*V1);

V = V(rindices);

However, after sorting, V became,

-8.05918955245067e-21 + 8.23317408693105e-22i

1.36822909718840e-15 - 1.33221528989010e-21i

1.01989680354965e-14 + 3.46136359467220e-21i

1.72392520759381e-14 + 1.86019192086409e-21i

1.23086553364893e-13 + 8.26560004261648e-21i

6.07212915777181e-13 + 2.79063028387683e-22i

1.32399364803625e-12 - 4.30261778360293e-21i

2.99051403313190e-12 + 3.62505072381834e-21i

4.68510672896002e-12 - 2.29503200085301e-21i

2.07808170074765e-11 - 2.84966374048803e-22i

7.32973689738923e-11 - 4.65099992985255e-21i

3.50507467296844e-10 - 1.10159115820306e-21i

2.28802604174547e-09 + 1.73500648980058e-20i

4.29713831923512e-09 + 3.73908633968205e-21i

2.80343931756963e-08 + 1.23048032017686e-20i

6.99991469893008e-08 - 1.02450891500650e-20i

6.28618594970652e-06 - 5.04267327744353e-20i

8.73059513582096e-06 + 1.23064435626381e-20i

1.28038961421133e-05 + 7.36148671834500e-20i

1.71925856406516e-05 - 1.15719050036467e-20i

1.95849840201760e-05 + 1.48445834874224e-20i

2.20073577954736e-05 - 5.80181618012595e-21i

2.23684164933882e-05 + 4.04939694038624e-21i

6.30592283269993e-05 - 7.50552502780072e-20i

0.000269899528923458 - 6.15654463989809e-20i

0.000800293022988111 + 1.22052572461947e-20i

0.00107796253204560 - 4.70645642035523e-20i

0.00117784972186107 + 2.08922253853130e-19i

0.00142769822781175 + 5.39004850343165e-20i

0.00147928037481547 - 2.74849838261212e-20i

0.00190176141109370 + 2.84699448762080e-19i

0.00192283028876372 + 2.81043109217511e-19i

which is defintely not in descending order.

I also tried on positive real numbers,

V1=[2;6;4;3;1;8];

[junk1, rindices1] = sort(-1*V1);

and the consequence is correct.

I don't know why the sorting of the complex numbers seems wrong.

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Answer 1

Cris LaPierre 2021-11-15

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1587069-problem-in-sorting-the-elements-of-a-complex-column-vetor-in-descending-order#answer_831954

编辑：Cris LaPierre 2021-11-15

在 MATLAB Online 中打开

Just specify 'descend' for your sort order.

B = sort(___,direction)

format longE
V=[0.00192283028876372 + 2.81043109217511e-19i
00190176141109370 + 2.84699448762080e-19i
00147928037481547 - 2.74849838261212e-20i
00142769822781175 + 5.39004850343165e-20i
00117784972186107 + 2.08922253853130e-19i
00107796253204560 - 4.70645642035523e-20i
000800293022988111 + 1.22052572461947e-20i
000269899528923458 - 6.15654463989809e-20i
30592283269993e-05 - 7.50552502780072e-20i
23684164933882e-05 + 4.04939694038624e-21i
20073577954736e-05 - 5.80181618012595e-21i
95849840201760e-05 + 1.48445834874224e-20i
71925856406516e-05 - 1.15719050036467e-20i
28038961421133e-05 + 7.36148671834500e-20i
73059513582096e-06 + 1.23064435626381e-20i
28618594970652e-06 - 5.04267327744353e-20i
99991469893008e-08 - 1.02450891500650e-20i
80343931756963e-08 + 1.23048032017686e-20i
29713831923512e-09 + 3.73908633968205e-21i
28802604174547e-09 + 1.73500648980058e-20i
50507467296844e-10 - 1.10159115820306e-21i
32973689738923e-11 - 4.65099992985255e-21i
07808170074765e-11 - 2.84966374048803e-22i
68510672896002e-12 - 2.29503200085301e-21i
99051403313190e-12 + 3.62505072381834e-21i
32399364803625e-12 - 4.30261778360293e-21i
07212915777181e-13 + 2.79063028387683e-22i
23086553364893e-13 + 8.26560004261648e-21i
72392520759381e-14 + 1.86019192086409e-21i
01989680354965e-14 + 3.46136359467220e-21i
-8.05918955245067e-21 + 8.23317408693105e-22i
36822909718840e-15 - 1.33221528989010e-21i];
newV = sort(V,'descend')
newV = 
922830288763720e-03 + 2.810431092175110e-19i
901761411093700e-03 + 2.846994487620800e-19i
479280374815470e-03 - 2.748498382612120e-20i
427698227811750e-03 + 5.390048503431650e-20i
177849721861070e-03 + 2.089222538531300e-19i
077962532045600e-03 - 4.706456420355230e-20i
002930229881110e-04 + 1.220525724619470e-20i
698995289234580e-04 - 6.156544639898089e-20i
305922832699930e-05 - 7.505525027800721e-20i
236841649338820e-05 + 4.049396940386240e-21i
200735779547360e-05 - 5.801816180125950e-21i
958498402017600e-05 + 1.484458348742240e-20i
719258564065160e-05 - 1.157190500364670e-20i
280389614211330e-05 + 7.361486718345000e-20i
730595135820959e-06 + 1.230644356263810e-20i
286185949706520e-06 - 5.042673277443530e-20i
999914698930080e-08 - 1.024508915006500e-20i
803439317569630e-08 + 1.230480320176860e-20i
297138319235120e-09 + 3.739086339682050e-21i
288026041745470e-09 + 1.735006489800580e-20i
505074672968440e-10 - 1.101591158203060e-21i
329736897389230e-11 - 4.650999929852550e-21i
078081700747650e-11 - 2.849663740488030e-22i
685106728960020e-12 - 2.295032000853010e-21i
990514033131900e-12 + 3.625050723818340e-21i
323993648036250e-12 - 4.302617783602930e-21i
072129157771810e-13 + 2.790630283876830e-22i
230865533648930e-13 + 8.265600042616479e-21i
723925207593810e-14 + 1.860191920864090e-21i
019896803549650e-14 + 3.461363594672200e-21i
368229097188400e-15 - 1.332215289890100e-21i
     -8.059189552450671e-21 + 8.233174086931050e-22i

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Cris LaPierre 2021-11-15

编辑：Cris LaPierre 2021-11-15

That is because your numbers are complex. You can find details here. By default, the sort function sorts complex values by their magnitude, and breaks ties using phase angles.

The magnitude is always positive. So while negating real numbers flips their order, that does not work for complex numbers because it doesn't change the sign of their magnitude.

奥刘 2021-11-16