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Solve equation (unrecognized function or variable)

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Alessandro Ruda
Alessandro Ruda am 10 Mai 2021
Kommentiert: Alessandro Ruda am 11 Mai 2021
Dear MatLab Comunity,
I have to solve this equation but it keeps saying that the variable 't' is unrecognized. I should have the plugins for the function 'solve' so I don't understand where is the problem.
N = 5.62
R = 6.40
W = 600
eqn = (10 + 2.*W.^(2).*t.^(2) - 8.*W.^(4).*t.^(4))./(10 +23.*W.^(2).*t.^(2) + 4.*W.^(4).*t.^(4)) -N./R
S = solve(eqn, t)
Any help would be appreciated!
All the best,
Alex

Akzeptierte Antwort

Stephan
Stephan am 10 Mai 2021
Bearbeitet: Stephan am 11 Mai 2021
% define t as symbolic
syms t
N = 5.62;
R = 6.40;
W = 600;
eqn = (10 + 2.*W.^(2).*t.^(2) - 8.*W.^(4).*t.^(4))./(10 +23.*W.^(2).*t.^(2) + 4.*W.^(4).*t.^(4)) -N./R
eqn = 
S = solve(eqn, t)
S = 
% scalar solutions, only real
S1 = vpasolve(eqn,t, [-Inf Inf])
S1 = 
  3 Kommentare
Stephan
Stephan am 11 Mai 2021
Then use:
% define t as symbolic
syms t
N = 5.62;
R = 6.40;
W = 600;
eqn = (10 + 2.*W.^(2).*t.^(2) - 8.*W.^(4).*t.^(4))./(10 +23.*W.^(2).*t.^(2) + 4.*W.^(4).*t.^(4)) -N./R
eqn = 
% scalar solutions, only real
S1 = vpasolve(eqn,t, [-Inf Inf])
S1 = 
change bounds from -Inf to zero to get only the positive solution:
S2 = vpasolve(eqn,t, [0 Inf])
S2 = 
0.00042280651261763657433032919695881
Alessandro Ruda
Alessandro Ruda am 11 Mai 2021
Thanks Stephan!

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