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

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Dingyu Xue
Dingyu Xue 2017-8-17
评论： Dingyu Xue 2017-8-25
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.

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Stefan Wehmeier
Stefan Wehmeier 2017-8-25
It is a matter of taste if you prefer results in terms of exp or sin. You could do
simplify(rewrite(A1, 'sin'))
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Dingyu Xue
Dingyu Xue 2017-8-25
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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