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# Syntax error in simulink

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Quamar Niyaz on 18 Jul 2016
Commented: Mark McBroom on 14 Nov 2020
Getting syntax error in Simulink for this expression
m*(u(1)-l*u(3)*u(3)*sin(u(2))+l*u(4)*cos(u(2)))
The equation seems correct. Can anyone explain it?

#### 6 Comments

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Walter Roberson on 19 Jul 2016
When I copy and paste your code into a Fcn block or Interpreted Fcn block in R2016a, I am not told of any error.
Quamar Niyaz on 20 Jul 2016
I am trying to implement this example http://ctms.engin.umich.edu/CTMS/index.php?example=InvertedPendulum&section=SimulinkModeling. I have followed the procedure as specified in it, but getting the errors in the third function block which is as follows:
The expression: m*(u(1)-l*((u(3))^2)*sin(u(2))+l*u(4)*cos(u(2)))
in 'Sim_Exp7/Subsystem/Subsystem/N' has a syntax error
I have also attached my mdl and error files. My Matlab version is R2015b.
Shoanaliy Arul on 12 Nov 2020
I am also getting the simular error.
Mine says:
The expression: m*(u(1) - l*u(3)*u(3)*sin(u(2)) + l*u(4)*cos(u(2))) in 'Pend_Model/Subsystem/N' has a syntax error

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### Answers (1)

Mark McBroom on 14 Nov 2020
The following variables need to be defined in the MATLAB workspace:
I, g, b, m, l, M
thetadot is missing a paren. It hsould be:
1/I*(-u(1)*cos(u(3)) - u(2)*sin(u(3)))

#### 1 Comment

Mark McBroom on 14 Nov 2020
Note. I debugged this by cutting and pasting each of the equations into the MATLAB workspace. This gives more detailed info on undefined variables and syntax errors.

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R2015b

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