MATLAB Answers

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

1 view (last 30 days)
HN
HN on 21 Oct 2020
Commented: Steven Lord on 21 Oct 2020
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 !

  0 Comments

Sign in to comment.

Accepted Answer

Matt J
Matt J on 21 Oct 2020
Probably because you copy-pasted the values of M from the screen to one of the scripts.

  3 Comments

Sign in to comment.

More Answers (1)

Steven Lord
Steven Lord on 21 Oct 2020
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.

  2 Comments

HN
HN on 21 Oct 2020
Steven Lord , Thank you. You are right ! What confuses me was the contraditing result between matlab live script and matlab scrpt.
Steven Lord
Steven Lord on 21 Oct 2020
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?

Sign in to comment.

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by