software request which works with symbolic transfer function

Since MATLAB doesnt work with symbolic transfer functions, do any of you know any software for this purpose??

Answer 1

[Walter Roberson]

The MATLAB Symbolic Toolkit permits symbolic transfer functions.

[Gustavo Reche]

really ? So why do I get errors like this when trying to build an transfer function with symbolic variables:

syms k

>> G=tf(1,[2 k])

Error using tf (line 287)
The values of the "num" and "den" properties must be row vectors or cell arrays of row vectors, where each vector is nonempty and containing numeric data. Type
"help tf.num" or "help tf.den" for more information.

If I try to define the transfer function in another way, I get something similar:

>> s=tf('s')

>> G=(s+1)*(s+k)

Error using  +  (line 63)
Invalid operand. Variables of type "sym" cannot be combined with other models.

However, since you're saying that this is possible, could you tell me how?

[Walter Roberson]

I made no claim that the Control System Toolbox supported symbolic transfer functions, or that support was as extensive as for numeric models.

Supported transforms include laplace and fourier: http://www.mathworks.com/help/symbolic/functionlist.html#btgypuv-1 and the z transform

There is support for heaviside and dirac: http://www.mathworks.com/help/symbolic/functionlist.html#btgypvv-1

Laplace example:

http://www.mathworks.com/matlabcentral/answers/136729-mupad-symbolic-ilaplace-high-order-transfer-function-to-time-domain

Helper function:

http://www.mathworks.com/matlabcentral/fileexchange/27302-syms-to-tf-conversion

If you are looking for more extensive tools, then I know that Maplesoft's Maple has a Dynamic Systems package for linear systems (I did not check about non-linear systems.)