Why matlab live editor and matlab script gives different rank calculation result for the same matrix ?

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HN 2020-10-21

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评论： Steven Lord 2020-10-21

I suddenly found matlab is misundesrstanding this matrix and checked it with matlab live editor. Then, matlab live gives the right rank .Why is that happened ? appreciated !

M =[-0.0000    0.0000         0         0         0   -0.0000;...
   -0.0000    0.0000          0         0         0   -0.0000;...
         0         0     1.0000         0         0         0;...
         0         0         0     1.0000         0         0;...
         0         0         0         0     1.0000         0;...
    0.0000    0.0000         0         0         0    0.0000]

Thank you !

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Answer 1

Matt J 2020-10-21

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Probably because you copy-pasted the values of M from the screen to one of the scripts.

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Matt J 2020-10-21

Since you accept-clicked my answer, it appears that you solved the problem?

HN 2020-10-21

编辑：HN 2020-10-21

Thank you Matt J , yes the problem is solved. You were right. What puzzeles me was the difference.

Thanks a lot 1

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Answer 2

Steven Lord 2020-10-21

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在 MATLAB Online 中打开

The value MATLAB displays is sometimes not the value MATLAB uses in computations.

>> format short
>> x = 1 + 1e-8
x =
    1.0000
>> x == 1
ans =
  logical
   0
>> y = x - 1
y =
   1.0000e-08
>> format longg
>> x
x =
                1.00000001

Under the short display format, even though x is not equal to 1 it is displayed as 1.0000. If it were exactly one, y would be exactly 0. When I change the display format to longg, you can see that it is not exactly one.

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HN 2020-10-21

Steven Lord , Thank you. You are right ! What confuses me was the contraditing result between matlab live script and matlab scrpt.

Steven Lord 2020-10-21

Is one using the computed value of x and one the displayed value via copy and paste? How are you ensuring you're using the exact same values, down to the last bit, in the two programs?

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