solve: Explicit solution could not be found

Question

I'm struggling to solve a system equation using the Matlab R2011a Symbolic Toolbox. The system belongs to a mechanism that already exists and I want to calculate its basic coordinates points, on the equations I have 13 unknown variables, 14 equations and 1 inequality. After I execute the code below and the Matlab answer is

Explicit solution could not be found

What I guess is that maybe the system needs more information, independent equations or something that I found called "assumptions", but I'm not sure how to interpret this answer... Looking on another questions I saw "mupad Notebook", but I see the same as the command window but more pretty (I read that is more precise but for my problem I don´t think it will help), isn´t it? So, basically my question is what does this Matlab answer really mean and how can I fix or help Matlab solve it.

S = solve(...
        '(xa-x0)^2+(ya-y0)^2-l2^2',...
        '(xa-x0)*(xc-xa)+(ya-y0)*(yc-ya)-l2*lac*cos(alpha1)',...
        '(xa-x0)*(xb-xa)+(ya-y0)*(yb-ya)-l2*lab*cos(alpha2)',...
        '(xg-xa)^2+(yg-ya)^2-lag^2',...
        '(xf-xc)^2+(yf-yc)^2-l6^2',...
        '(xd-xb)^2+(yd-yb)^2-l3^2',...
        '(xe-xa)^2+(ye-ya)^2-lae^2',...
        '(xe-xd)*(xf-xe)+(ye-yd)*(yf-ye)-lef*lde*cos(alpha3)',...
        '(xf-xe)*(xd-xf)+(yf-ye)*(yd-yf)-lef*ldf*cos(alpha4)',...
        '(xd-xf)*(xe-xd)+(yd-yf)*(ye-yd)-ldf*lde*cos(alpha5)',...
        '(xg-xa)*(xe-xg)+(yg-ya)*(ye-yg)-lag*leg*cos(alpha6)',...
        '(xe-xg)*(xa-xe)+(ye-yg)*(ya-ye)-leg*lae*cos(alpha7)',...
        '(xa-xe)*(xg-xa)+(ya-ye)*(yg-ya)-lae*lag*cos(alpha8)',...
        '(xe-xg)^2+(ye-yg)^2-leg^2',...
        'xg>0',...
        'xa', 'ya', 'xb', 'yb', 'xc', 'yc', 'xd', 'yd', 'xe', 'ye', 'xf', 'yf', 'xg'...
        );

Warning: 15 equations in 13 variables. 
> In C:\Program Files\MATLAB\R2011a\toolbox\symbolic\symbolic\symengine.p>symengine at 52
  In mupadengine.mupadengine>mupadengine.evalin at 96
  In mupadengine.mupadengine>mupadengine.feval at 137
  In solve at 77
  In Chassis_coordinates_equations at 45
Warning: Explicit solution could not be found. 
> In solve at 83
  In Chassis_coordinates_equations at 45

Carl Witthoft Carl Witthoft · Accepted Answer · 2015-07-06T11:59:24

Read the warning: You have overdefined your system (more equations than variables), which means that unless several pairs of equations are actually the same function, there is no solution. That's a fundamental part of linear algebra.

You don't state where or how you came up with those equations, but it sure looks like you've got a poorly defined system in the first place. Try reorganizing your proposed system.

solve: Explicit solution could not be found

1 Answers