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A Fully Automated Flowgraph Analysis Tool for MATLAB


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A Fully Automated Flowgraph Analysis Tool for MATLAB



22 Mar 2005 (Updated )

A handy signal flow graph analysis tool for exploring transfer function(s) of a given system.

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A tool for generating one or several transfer functions for a given system. Applicable for both continuous- and discrete-time systems. System can also be purely symbolic.
This is a tool for generating transfer function information with ease. It is based on a nodelist presentation of a system which makes the exploring of the transfer function information less prone for errors.

The tool reads a user-defined textual nodelist which defines the signal flow graph of a system and then generates the needed transfer function(s).

The tool is generic so that it is easily applicable for many purposes. Tool can be applied to digital filter design, circuit design, delta-sigma modulator analysis or even reflection analysis s-parameter measurements in RF techniques and in optics.

The package includes 10 examples of nodelist files and some of them are presented in the manual. It also includes a useful extension: a parameter solving tool for e.g. filter design.

Requires Matlab 6 or higher and optionally control system toolbox (the tool has an optional output for an LTI-model).


This file inspired Flow Graph Analysis Tool Gui.

Required Products Control System Toolbox
Symbolic Math Toolbox
MATLAB release MATLAB 8.2 (R2013b)
Other requirements Control System Toolbox is optional but for some examples it is required.
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Comments and Ratings (9)
02 May 2014 Marko Neitola

Thank you Weiming XIONG for the suggestion.

The tool should now work in newer Matlab versions.

08 Jan 2014 Weiming XIONG

Adding 'find' in 4 lines of flow_tf.m seems fixing it:

line 131~132:

line 141~142: innod(find(innod==sym(char(innod(ind)))))=ym_ind;

30 Sep 2013 Marko Neitola

Hi Steffen,

Thanks for notifying the problem.
It is likely that I will try to fix this problem, but not very soon. In the mean time, I won't remove the tool from File Exchange.

For other flowgraph analysis tool users: if you have suggestions on how to fix the problem, please send info to me: marko.neitola(at)

Br, Marko

14 Jun 2013 Steffen

Hi Marko.
Thanks for that interesting tool. Unfortunately it does does not work with R2013a (even with the example files). Following error message is thrown:

Error using symfun>validateArgNames (line 191)
Second input must be a scalar or vector of unique symbolic variables.
Error in symfun (line 45)
y.vars = validateArgNames(inputs);
Error in sym/subsasgn (line 1639)
C = symfun(B,[inds{:}]);
Error in flow_tf (line 131)
Error in flowdemo (line 5)

Would you please provide me some help on this issue?

30 Mar 2010 Eric

Thank you, Marko! I haven't tried it yet, but this kind of tool is definitely useful!

09 Aug 2007 Marko Neitola

I made a GUI front-end for this tool. See the link in the acknowledgements-section.

08 Jan 2007 Eslam Abdel Razek Mohammed

yes its good for me

07 Nov 2005 Mikko Loikkanen

Very useful tool for everyone working with signal flow graphs. Only thing really missing is the ability to simplify complex analysis results.

10 Aug 2005 Maciej Borkowski

Well done. It saves a lot of time, especially when you experiment with different topologies. Thank you!


A bugfix preventing errors caused by an ascii-character (carriage return).

26 May 2005

Updated PDF manual in the zipped package.

27 Jul 2005

Improved the error messaging in the main program (easier to debug your system).

02 Feb 2006

Minor bugfixes in the error messaging. Also added new examples.

02 May 2014

Fixed a bug, thanks to the suggestion by Weiming XIONG.

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