Output a small number as zero

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S Crombie
S Crombie on 28 Feb 2018
Commented: Stephen23 on 1 Mar 2018
If I type cos(pi/2) the answer comes back as 6.1232e-17 where I know, of course, that the correct answer is zero. What is the best way to get MATLAB intelligently to output zero in place of these very small numbers?
This came up when I was computing a rotation matrix using angles which were simple fractions of pi and one of the elements returned was 24678615572571482867467662723121/6582018229284824168619876730229402019930943462534319453394436096
which ideally would have been rounded to zero.

Accepted Answer

Birdman
Birdman on 28 Feb 2018
Edited: Birdman on 28 Feb 2018
Firstly, you need to read this:
Then, you may do this:
a=cos(pi/2);
if abs(a)<1e-6
a=0;
end
Note that 1e-6 is a tolerance value that user specifies, you can change it if you want.
  5 Comments
Stephen23
Stephen23 on 1 Mar 2018
" Is it treating my matrix as if it's composed of text strings?"
If they are symbolic variables then it is treating them as symbolic variables. Most likely the problem is how you define those symbolic variable values, e.g. first defining them as double before converting to symbolic, but unless you show us your code then we will have to rely on our magic crystal balls to know.
If you want help then ask a new question and give a minimum working example.

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