an error in new versions? triognometric function of A*t

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Dingyu Xue
Dingyu Xue on 17 Aug 2017
Commented: Dingyu Xue on 25 Aug 2017
Please run the following code in MATLAB R2017a
A1=simplify(A1), A2=simplify(A2)
A=[-7,2,0,-1; 1,-4,2,1; 2,-1,-6,-1; -1,-1,0,-4];
syms t, A1=(expm(A*1j*t)-expm(-A*1j*t))/(2*1j);
A2=(expm(A*1j*t)+expm(-A*1j*t))/2;
The results are different from the ones in earlier versions such as R2008a, R2011a. The results in earlier versions are consistent with the commands funm(A*t,'sin'). Obviously the results in the new versions are wrong, or at least not simplified well.

Accepted Answer

Stefan Wehmeier
Stefan Wehmeier on 25 Aug 2017
It is a matter of taste if you prefer results in terms of exp or sin. You could do
simplify(rewrite(A1, 'sin'))
  1 Comment
Dingyu Xue
Dingyu Xue on 25 Aug 2017
Yes, that works, thank you! It is not really the personal taste problem of sin rather than exp in this particular example. In the exp expression, terms with complex quantities are resulted, and anybody may prefer the simpler one without complex quantities, obtainable with your rewrite command, which was also the direct solution in old versions.

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