How to Simplify an symbolic expression
1 次查看(过去 30 天)
显示 更早的评论
Hi all, I want to simplify this equation
a= 2 atan((-2+Sqrt(4-gama^2 *l^2* M^2-4* gama *l* M^2 *tan(gama/2)+4* tan(gama/2)^2-4 *M^2 *tan(gama/2)^2))/(gama* l* M+2* tan(gama/2)+2* M* tan(gama/2)))
into this form
a= (gama/2)-asin(((gama*l*M)/2)*cos(gama/2)+M*sin(gama/2))
Can anyone help?
7 个评论
Torsten
2017-4-20
Or maybe this can help:
https://de.mathworks.com/help/symbolic/isequaln.html
Best wishes
Torsten.
回答(2 个)
Andrew Newell
2017-4-21
If I define
a= 2*atan((-2+sqrt(4-gama^2 *l^2* M^2-4* gama *l* M^2 *tan(gama/2)+4* tan(gama/2)^2-4 *M^2 *tan(gama/2)^2))/(gama* l* M+2* tan(gama/2)+2* M* tan(gama/2)));
b = (gama/2)-asin(((gama*l*M)/2)*cos(gama/2)+M*sin(gama/2));
and substitute pi for gama,
subs(a,gama,pi)
subs(b,gama,pi)
I get a==NaN and b==pi/2 - asin(M). So they are not the same. I find that applying simplify to a does not change it significantly.
5 个评论
Torsten
2017-4-21
I still don't understand why you try to transform the first expression into the second if - as you write - you are sure that both expressions yield the same values for a (at least in cases where both expressions are real-valued).
Best wishes
Torsten.
Walter Roberson
2017-4-21
I randomly substituted M=2, l=3. With those two values, the two expressions are not equal. One of the two goes complex from about gama = pi to gama = 17*pi/16 . From 17*pi/16 to roughly 48*Pi/41 the difference between the two is real valued . After that the difference has a real component of 2*pi and an increasing imaginary component.
8 个评论
Andrew Newell
2017-4-23
To summarize what Walter and I are saying, the two expressions are clearly not always equal, and the conditions under which they are equal are hard to pin down. Perhaps you should look more closely at how they did it in the article. Not that published work is always 100% correct.
另请参阅
类别
在 Help Center 和 File Exchange 中查找有关 Calculus 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!