Why do I get this error message: Undefined function or variable 'equationsToMatrix'.

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Zeyad Elsayed 2019-7-19

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https://ww2.mathworks.cn/matlabcentral/answers/472548-why-do-i-get-this-error-message-undefined-function-or-variable-equationstomatrix

评论： Walter Roberson 2019-7-20

Hello everyone,

I have written a code on a desktop at my University and I ran it and it worked. However, when I saved and ran the exact same code on my laptop it returns with the following error message:

Undefined function or variable 'equationsToMatrix'.
Error in Eq_Solver (line 54)
    [AA,BB] = equationsToMatrix([eq1, eq2, eq3, eq4],[A1, B1, A2, B2])

I searched about it and I saw some people in the community mentioning that this may be because of not having Symbolic Math Toolbox installed. When I checked the addons explorer, I found the Symbolic Math Toolbox installed, however when I typed "ver" in the command window I did not see Symbolic Math Toolbox installed.

MATLAB                                                Version 9.5         (R2018b)
Simulink                                              Version 9.2         (R2018b)
Control System Toolbox                                Version 10.5        (R2018b)
DSP System Toolbox                                    Version 9.7         (R2018b)
Data Acquisition Toolbox                              Version 3.14        (R2018b)
Image Processing Toolbox                              Version 10.3        (R2018b)
Instrument Control Toolbox                            Version 3.14        (R2018b)
Optimization Toolbox                                  Version 8.2         (R2018b)
Signal Processing Toolbox                             Version 8.1         (R2018b)
Simulink Control Design                               Version 5.2         (R2018b)
Statistics and Machine Learning Toolbox               Version 11.4        (R2018b)

The code:

 syms t
 syms A1 B1 A2 B2
 Omega = 200;
 M11 = 5.0;
 M12 = 0;
 M21 = 0;
 M22 = 1.0;
 C11 = 3;
 C12 = -1;
 C21 = -1;
 C22 = 1;
 K11 = 400;
 K12 = -150;
 K21 = K12;
 K22 = 150;
 M = [M11 M12; M21 M22];
 C = [C11 C12; C21 C22];
 K = [K11 K12; K21 K22];
 F1 = 2*Omega^2;
 F2 = 0.1*Omega^2;
 F = [F1*sin(Omega*t); F2*cos(Omega*t)];
 eq1 = K11*(B1) + K12*(B2) - M11*(B1*Omega^2) - M12*(B2*Omega^2) + C11*(A1*Omega) + C12*(A2*Omega) == 0;
 eq2 = K11*(A1) + K12*(A2) - M11*(A1*Omega^2) - M12*(A2*Omega^2) + C11*(-B1*Omega) + C12*(-B2*Omega) == F1;
 eq3 = K21*(B1) + K22*(B2) - M21*(B1*Omega^2) - M22*(B2*Omega^2) + C21*(A1*Omega) + C22*(A2*Omega) == F2;
 eq4 = K21*(A1) + K22*(A2) - M21*(A1*Omega^2) - M22*(A2*Omega^2) + C21*(-B1*Omega) + C22*(-B2*Omega) == 0;
 [AA,BB] = equationsToMatrix([eq1, eq2, eq3, eq4],[A1, B1, A2, B2]);