Help to understand a strange behaviour

2 views (last 30 days)
Ivan
Ivan on 1 Apr 2012
WTF is the following: (noticed ocationally)
>> clear
>> sind(30)
ans =
-0.8660
>> whos
Name Size Bytes Class Attributes
ans 1x1 8 double
after restart:
>> sind(30)
ans = 0.5000
(R2010b)
  5 Comments
Ivan
Ivan on 2 Apr 2012
plot looks like normal, but drops to -1 at -720:
>> sind(-720)
ans =
-1

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Accepted Answer

Jan
Jan on 2 Apr 2012
I asked Google for "Matlab bug sind" and found:
My conclusion: Ask MathWorks for a bugfix of your version. It is easy to insert a workaround as M-file in your toolbox folder:
function Y = sind(X)
Y = sin(X * 0.017453292519943295769236954843959);

More Answers (2)

Jan
Jan on 1 Apr 2012
Does
which sind -all
reveal any unexpected details?
  2 Comments
Ivan
Ivan on 2 Apr 2012
The two contiguous commands give:
>> sind(30)
ans =
0.500000000000000
>> sind(30)
ans =
-0.866025403784439

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Ivan
Ivan on 2 Apr 2012
Thank you, Jan. Yes, i'm now using sin with argument in radians and that's ok. But this issue made me suspicious about all my results ever got with MatLab... Its very sad (
  1 Comment
Jan
Jan on 2 Apr 2012
I agree that such bugs reduce the confidence. Therefore it would be great great great, if MathWorks offers a similar service as most other programs: Automatic download of patchs and bugfixes. Even a dynamically created list of known bugs would be helpful, while the bugs list at http://www.mathworks.com/support/bugreports/ is still too hidden for standard users. In addition it is weak: I do not find a report when I'm searching for "sind" on "all releases". Is it possible that this bug has not been reported?
It seems like this bug is either not reproducible or there is no or a not sufficiently powerful unittest for the elementary functions.
Please contact the technical support. The more votes they get the better for the users and the company.

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