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A Fully Automated Flowgraph Analysis Tool for MATLAB

4.0 | 2 ratings Rate this file 16 Downloads (last 30 days) File Size: 83.2 KB File ID: #7224 Version: 1.3
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A Fully Automated Flowgraph Analysis Tool for MATLAB


Marko Neitola (view profile)


22 Mar 2005 (Updated )

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

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This tool is based on a textual signal flowgraph (SFG) nodelist presentation of a system. This makes the exploring of the transfer function information quite fast and easy. Applicable for both continuous- and discrete-time systems. System can also be purely symbolic.
The tool reads a user-defined textual SFG which defines the signal flow graph of a system and then generates the needed transfer function(s). Alternatively outputs an SFG system matrix that can be used for further study.

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 for parameter extraction: a function for extracting a system of equations.

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 8.4 (R2014b)
MATLAB Search Path
Other requirements Control System Toolbox is optional but for some examples it is required. Manual.pdf discusses the potential problems with older matlab versions (R6 to R8a).
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Comments and Ratings (9)
02 May 2014 Marko Neitola

Marko Neitola (view profile)

Thank you Weiming XIONG for the suggestion.

The tool should now work in newer Matlab versions.

Comment only
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;

Comment only
30 Sep 2013 Marko Neitola

Marko Neitola (view profile)

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

Comment only
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?

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30 Mar 2010 Eric

Eric (view profile)

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

Comment only
09 Aug 2007 Marko Neitola

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

Comment only
08 Jan 2007 Eslam Abdel Razek Mohammed

yes its good for me

Comment only
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.

09 Dec 2014 1.1

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

10 Dec 2014 1.3

-Manual update: help with older MATLAB versions
-System matrix as output option
-parameter solver replaced

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