SYMBOLIC system of equations

Hello,

I'd like to know if there's a way in MATLAB to solve a symbolic system of equations with symbolic coefficients ?

Thanks for your help.

Answer 1

[Grufff]

Yes, the symbolic math toolbox will do this. Type mupad at the matlab command prompt, then dig into the help files and documentation to find your feet.

Overview and examples here:

http://www.mathworks.co.uk/products/symbolic/examples.html

http://www.mathworks.co.uk/discovery/mupad.html

[hugg]

Thanks Gruff for your prompt answer.

I am currently looking into Mupad.

I need a function equivalent to linsolve to solve a fully symbolic linear system of equations (the unknowns as well as the coefficients are Symolic). I am not sure this is handled by Matlab, but I may be mistaken (I hope).

Thanks for your help.

[Walter Roberson]

solve() should be able to do it.

[hugg]

Thanks Walter. However solve does not deal with matrix forms (please correct me if I am mistaken).

I have a matrix expression :

A.X = B

All matrices are symbolic. Is there a function in matlab to solve the above equation for X (A and B are parameters).

Thanks.

[Walter Roberson]

I think I read that as of R2012a, you can use the \ operator on symbolic arrays.

Otherwise, you can do the symbolic matrix multiply and solve() that.

[hugg]

I have R2009b version.

I'm not sure I get what you said regarding the \ ? (do mean to devide vector B by matrix A ?).

I think that if there is no function dealing with matrix symbolic linear equation I will rewrite it as a system of polynomial expressions.

Thanks again !

[Walter Roberson]

Notice that in the (current) linsolve documentation http://www.mathworks.com/help/symbolic/linsolve.html that the example involves symbolic A and B, which is what you are looking for.

[hugg]

Thank you Walter.

I looked into it. It seems you are right.

[hugg]

I tried the example http://www.mathworks.com/help/symbolic/linsolve.html on my Matlab and it generates this error message : "??? Undefined function or method 'linsolve' for input arguments of type 'sym'.".

I guess this is due to the old version of Matlab I am running (R2009b).

It looks like I got the answer to my question.

Thank you guys for your answers.

[Walter Roberson]

You might be able to find something in MuPADs linalg library. http://www.mathworks.com/help/symbolic/mupad_ug/using-the-mupad-libraries.html and http://www.mathworks.com/help/symbolic/mupad_ug/linear-algebra-library.html

Search your documentation for "standard library", as you will get a very different document (that has been removed in R2012b). http://www.mathworks.com/help/releases/R2009b/toolbox/mupad/linalg/ and http://www.mathworks.com/help/releases/R2009b/toolbox/mupad/stdlib/