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Warning: The solutions are parameterized by the symbols: z

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Hi There
This is my first time posting, as i am new to matlab, so apologies if i have missed some etiquette that i know there is on some forums.
i am trying to calculate some values for angles of a mechanical arm with a linkage system. i have drawn out the system and found all the relationships i possibly can using the cosine rule and put them all into the file, hence some are not applicable to this bit of code.
my problem is i am trying to use the solve function to solve the following equation for zeta;
k2=sqrt(s^2+h^2-2*s*h*cos(theta+zeta))
i can find the solution of this using wolframalpha as;
zeta=-acos((h^2-k^2+s^2)/(2*h*s))-t
however if i write solve(k2, zeta) it comes up with the following error;
Warning: The solutions are parameterized by the symbols: z7.
To include parameters and conditions in the solution, specify the 'ReturnConditions' option.
> In solve>warnIfParams (line 500)
In solve (line 356)
Warning: The solutions are valid under the following conditions: (in((theta + z7 + acos((H^2 + 270400)/(1040*H)))/(2*pi), 'integer') | in((theta + z7 - acos((H^2 + 270400)/(1040*H)))/(2*pi), 'integer')) & -1 <= (H^2 +
270400)/(1040*H) & (H^2 + 270400)/(1040*H) <= 1 & 0 < z7.
To include parameters and conditions in the solution, specify the 'ReturnConditions' option.
> In solve>warnIfParams (line 507)
In solve (line 356)
I know that the answer for theta and zeta are 0.271 and 0.757 at the point where l is 330, i could just write in what the rearrangement is but that kind of defeats the object of having a maths package in my eyes and i would like to know for future knowledge what i'm doing wrong.
Hopefully someone can help me by telling me i'm an idiot and i've missed something stupid.
Ross
  1 comentario
Ross Hanna
Ross Hanna el 19 de Abr. de 2017
ok, so i've got past the first problem which is getting matlab to give me an answer other than "z". i did this by making theta and zeta "real" when writing syms. the problem now is its giving me two answers, one positive, one negative. i have tried B=A(A=>0) but it doesnt work. i have tried "assume" but it comes up with the error message
Undefined function 'assume' for input arguments of type 'logical'
any help would be greatly appreciated. thanks

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Andrew Newell
Andrew Newell el 19 de Abr. de 2017
The function solve is part of the Symbolic Math Toolbox. Are you defining the symbolic variables? If I run this code
syms s h theta zeta
k2=sqrt(s^2+h^2-2*s*h*cos(theta+zeta));
zeta = solve(k2, zeta)
I get
zeta =
- theta - acos((h^2 + s^2)/(2*h*s))
acos((h^2 + s^2)/(2*h*s)) - theta
  2 comentarios
Ross Hanna
Ross Hanna el 20 de Abr. de 2017
Editada: Ross Hanna el 20 de Abr. de 2017
Thanks for replying. Yes i am defining symbolic variables, not sure if this is the best way but i don't know their values without consulting a 3d model which i am trying to recreate and this is the only way of calculating them.
my problem is that when i run the program it gives me the answers above, but then lower down it has the issue of the error below;
Error using mupadengine/feval (line 163) The number of equations exceeds the number of indeterminates. This is allowed only for polynomial systems.
this is i'm guessing as sol_zeta is giving two outputs. how do i limit solve to one output? thanks
Andrew Newell
Andrew Newell el 20 de Abr. de 2017
If this problem is well formulated, you could try both values of zeta, one at a time, and then determine whether one of them can be ruled out by the mechanical constraints. If not, you may need to think about the physics some more!

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