Solve returning root but doesn't give a numerical expression.
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Boris Huljak
el 28 de Abr. de 2016
Respondida: pepe
el 23 de Dic. de 2019
Hello ! I'm actually using the function " solve ", but instead of returning an expression, i get the following : "
9
root(z^4 - (10*z^3)/9 - z^2/6561 - z/729 - 91/6561, z, 1)
root(z^4 - (10*z^3)/9 - z^2/6561 - z/729 - 91/6561, z, 2)
root(z^4 - (10*z^3)/9 - z^2/6561 - z/729 - 91/6561, z, 3)
root(z^4 - (10*z^3)/9 - z^2/6561 - z/729 - 91/6561, z, 4)
These are indeed the solutions, but why it doesn't express it ? If i use the function " roots " with a vector with the above coefficient, it gives me the solution numerically. Anyone have a way to either get the answer numerically, or to extract the coeffcient of the above expression automatically ? In any case, here is the simple code :
clear all
syms a
b=9;h=0.1;
t2=a^4*b^3-b-h*(b^3-b^5*a^4)-(b^4*a^3-a-h*(a^3-b^4*a^5))
sol=solve(t2,a)
Thanks !
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Walter Roberson
el 28 de Abr. de 2016
sol = solve(t2, a, 'MaxDegree', 4)
You should consider the possibility that you are using the wrong tool. solve() is for finding exact solutions. Your h is a floating point number rather than being 1/sym(10), which suggests that you are not interested in exact solutions. You should be giving consideration to using vpasolve() instead of solve()
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pepe
el 23 de Dic. de 2019
I have had a similar version dependent exprience. My code is:
syms x
solve(x^3+x-1==0)
In Matlab 2019 it produces the useless root() output that you also mentioned. But in MATLAB 2014 it produces a nicer result comprised of fractions and sums of numbers;...so I recommend you also give it a try using an old version of MATLAB.
good luck
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