How do i transfer big symbolic equations into Simulink

Hello everyone,

I am trying to solve the dynamics of a serial manipulator with 6DOF, and I want to transfer the result of an m file (vector of symbolic Torques) into a Simulink block and replace the symbolic variables with a vector of input to have the final numeric result as an output of the block.

I tried a Matlab function block but it does not support symbolic variables.

I tried to call the function as an extrinsic function but Simulink crashes every time I run it.

"from workspace" and "from m file" blocks are not what I need since I have an input to the block.

Any suggestions?

Thanks in advance.

[Stefan Raab]

Hello,

I did the following: I created a sym variable

s = sym(3)

and tried to assign its value to a constant block in Simulink: If the constant value is simply chosen to be "s", the following error occurs:

"Invalid setting in 'untitled/Constant' for parameter 'Value'",

but when I tried "double(s)" as constant value, it worked fine and a Display block connected to the Constant block showed the correct value of 3 in the simulation.

I hope this might help you. If not, could you please describe your problem more detailed?

Kind regards, Stefan

[Sed]

hello Stefan,

I cannot use a constant block because it only has an output, no input.

I have this huge symbolic vector, I want to put it in a simulink block with an input and output, so that the input replaces all the symbols in the vector and displays a numeric one in the output.

let's say I have the following:

syms q1

syms q2

syms dq1

syms dq2

T=[cos(q1)+sin(q2)*dq1 ; son(q2)*dq2]

I want symbolic T to be in a block and the vector [q1;q2;dq1;dq2] to be an input to this block. matlab function would do it but it doesn't support symbols.

I also can't not use symbols because I have some derivations in the code.

I tried to copy the massive symbolic T vector in a matlab function but it's so big that simulink crashes every time I run it.

[Negin Borna]

Hello sed, I have same problem,can you explain how you fixed it?

Answer 1

[Ced]

What do you mean by "matlab function does not support symbols"? Maybe I misunderstood your problem, but there is a function called matlabFunction, and it is specifically made to take symbolic expressions and turn them into "numerical functions".

Here is a small example for a 3DOF robot arm:

% Given: symbolic EoM dx = f(....)
syms q1 q2 q3 dq1 dq2 dq3 T1 T2 T3 real
q = [q1 q2 q3]';      % generalized coordinates
dq = [dq1 dq2 dq3]';  % derivative of generalized coordinates
T = [T1 T2 T3]';      % torque vector

% ... HERE: computation of EoM, returning symbolic dx = f(q,dq,T)

% now generate function
matlabFunction(dx,'file','f_dyn','vars',{[q;dq],T});

This will generate a file f_dyn.m with function

function dx = f_dyn(in1,in2)

where in1 = [ q ; dq ] and in2 = T

[Sed]

hello, thank you for your answer. it works for most of the equations, but mine results in a massive vector, so when I tried to generate the matlabFunction it took such a long time (more than an hour) that I had to stop it.

any alternatives?

[Sed]

hello again,

I am still struggling to make it work but I got the idea (it took a long time to generate the function but it worked), I just was not very familiar with the use of a matlabfunction.

thank you for your help.

[Ced]

Great, thanks for the update.

[Negin Borna]

Hello I faced same problem I have 5*5 matrices and I should take partial derivative of this matrices, and take the derivative of matrices in m file, now I dont know how should send the data (5*5 symbolic matrix) from m file to simulink.. can any one help me!

[Walter Roberson]

matlabFunction() and be sure to use 'file' and 'optimize', false

[Negin Borna]

Hello roberson, Many thanks, i have a question,I try to converts the symbolic function in mfile with matlabFunction. Now how i can use this function in simulink? ( this function is one input of simulink model)

[Walter Roberson]

Use a MATLAB Function Block and call the function from that.

As usual it is best to pre-allocate the space for the outputs before calling the file.

[Negin Borna]

Hello Every one.. I do this method and use matlab function block to call matlabFunction and run simulink but one error shows “ output argument ‘matrix name’ is not assigned on some execution paths. What should I do and write in this block to fixed this error?

[Walter Roberson]

Please show the code for the function that reports that erroy