Solving a System of Equations with syms

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Kevin Bachovchin
Kevin Bachovchin 2013-2-14
Hello,
I have a system of 10 equations and 14 unknowns. I want to solve this system of equations for 6 particular unknowns in terms of the other unknowns.
When I use solve(Equations==0) then it successfully solves for 10 unknowns in terms of the other 4 unknowns. However, I can't control which 10 unknowns MATLAB solves for.
When I try to specify 6 of the unknowns MATLAB solves for and use solve(Equations==0,x1,x2,x3,x4,x5,x6) then I get an empty matrix as my answer.
Can someone please tell me how I can correctly specify the 6 unknowns that I want MATLAB to solve for?
Thank you, Kevin
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Walter Roberson
Walter Roberson 2013-2-14
Perhaps the equations are not solvable with respect to those 6 variables.
Kevin Bachovchin
Kevin Bachovchin 2013-2-14
编辑：Walter Roberson 2013-2-14
Seems like I have to specify all 10 substitution variables for solving the other 4 variables, but I think that is ok for my purpose.
When I used, solve(Equations==0,x1,x2,x3,x4,x5,x6,x7,x8,x9,x10), then that successfully solves for x11,x12,x13,x14.
Do you know is there a way to specify the substitution variables as a matrix? Doing
XSubsitute = [x1,x2,x3,x4,x5,x6,x7,x8,x9,x10]
solve(Equations==0,XSubstitute)
produces an empty matrix as my answer.
I really need to be able to specify the substitution variables as the elements in the matrix to be able to apply my code for a general problem.

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Walter Roberson
Walter Roberson 2013-2-14
编辑：Walter Roberson 2013-2-14
XSubstitute = {x1,x2,x3,x4,x5,x6,x7,x8,x9,x10}
solve(Equations==0,XSubstitute{:})
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Kevin Bachovchin
Kevin Bachovchin 2013-2-14
The problem with this is that I lose the field names then. There's no way to directly extract the first N fields and values from a struct and then put in another struct? Something like answer2 = answer{1:N}?

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