Solve returns empty result although solution exists
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Hello I'm trying to solve the following system of equations,
This should be easy to solve by hand. However using solve returns an empty sym struct. what am i missing here?
variables used are attached.
Thank you.
EDIT: re-uploaded variables and added code.
EDIT2:provided working example as per @Walter Roberson's comment.
5 个评论
Star Strider
2019-3-19
Your .mat file fails. It is impossible to read its contents.
Post or attach your code as a text .m file, and attach your data in a readable form (.txt, .mat, or something else).
Walter Roberson
2019-3-19
Is it possible that you have Maple installed on your system?
Hazem Abdelghany
2019-3-19
Hazem Abdelghany
2019-3-19
编辑：Hazem Abdelghany
2019-3-19
采纳的回答
Walter Roberson
2019-3-19
0 个投票
You are accidentally using Maple's sym() and solve() calls. The .mat you provided for us is only useable by people who have installed "MATLAB Connector for Maple" .
You need to use pathtool to give the Maple functions a lower priority than the MATLAB functions and recreate the equations matrix and try again.
5 个评论
Hazem Abdelghany
2019-3-19
Walter Roberson
2019-3-19
You have 15 equations in 14 variables and your system is inconsistent.
Walter Roberson
2019-3-19
Part of the reason for inconsistency is your use of floating point numbers.
[A,b] = equationsToMatrix(eqns);
sol = A(1:14,:)\b(1:14);
A*sol-b
The final inconsistent row will be about 1E-13. A single bad round-off in your floating point values could lead to that.
Hazem Abdelghany
2019-3-19
Walter Roberson
2019-3-19
编辑：Walter Roberson
2019-3-21
The lines above show a solution in which the only inconsistency is on the order of 1E-13 , The order of the variables in sol will be the same as symvar(eqns)
Note: if you vpa(eqn) and compare that to your posted equations, you will see that they do not round exactly the same way. The equations in your .mat are not exactly the same as you would get by converting your posted equations to rationals. That matters because the correction you would need to make the equations consistent is less than the difference in stored versus posted values -- whatever round-off you have going in creating those coefficients is causing problems.
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