Problem with solving the symbolic equation in Matlab; Warning: Explicit solution could not be found. > In solve at 179 [ empty sym ]]

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PhD_77 2013-9-24

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https://ww2.mathworks.cn/matlabcentral/answers/88089-problem-with-solving-the-symbolic-equation-in-matlab-warning-explicit-solution-could-not-be-found

评论： John D'Errico 2014-6-6

Dear all,

I would like to solve the following equation symbolically so that to make the variable ’alp2’ the subject of the equation ( e.g. alp2=….). Note that, the only unknown variable is ‘alp2’

qm=
(2^(1/2)*a1*a2*alp1*alp2*cdg*(rg1*(dp - g*hi*(alp1*rg1 - rw*(alp1 - 1)) - g*htt*(alp2*rg2 - rw*(alp2 - 1)) + g*hc*(- avg_rg^2 + rw*(alp1/2 + alp2/2 - 1))))^(1/2))/(a1^2*alp1^2*p - a2^2*alp2^2)^(1/2) + (2^(1/2)*a1*a2*cdw*(rw*(dp - g*hi*(alp1*rg1 - rw*(alp1 - 1)) - g*htt*(alp2*rg2 - rw*(alp2 - 1)) + g*hc*(- avg_rg^2 + rw*(alp1/2 + alp2/2 - 1))))^(1/2)*(alp1 - 1)*(alp2 - 1))/(a1^2*(alp1 - 1)^2 - a2^2*(alp2 - 1)^2)^(1/2)

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I wrote the following code, but the output message was [ empty sym ];

>> syms cdg rg1 rg2 dp a1 a2 alp1 alp2 p cdw rw g hi hc avg_rg avg_alpa htt;

>>solve(' qm=(2^(1/2)*a1*a2*alp1*alp2*cdg(rg1*(dp - g*hi*(alp1*rg1 - rw*(alp1 - 1)) - g*htt*(alp2*rg2 - rw*(alp2 - 1)) + g*hc*(- avg_rg^2 + rw*(alp1/2 + alp2/2 - 1))))^(1/2))/(a1^2*alp1^2*p - a2^2*alp2^2)^(1/2) + (2^(1/2)*a1*a2*cdw*(rw*(dp - g*hi*(alp1*rg1 - rw*(alp1 - 1)) - g*htt*(alp2*rg2 - rw*(alp2 - 1)) + g*hc*(- avg_rg^2 + rw*(alp1/2 + alp2/2 - 1))))^(1/2)*(alp1 - 1)*(alp2 - 1))/(a1^2*(alp1 - 1)^2 - a2^2*(alp2 - 1)^2)^(1/2)* ',alp2)

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The output after running the code was;

Warning: Explicit solution could not be found. 
> In solve at 179 
 ans =
 [ empty sym ]

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Any suggestions?

Kind regards

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PhD_77 2014-6-6

any help please?!

John D'Errico 2014-6-6

And do you expect that an analytical solution MUST exist for any possible problem you might pose? Sorry, but magic only happens for Harry Potter, unless of course, you happen to have a magic wand.

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