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<p>David,</p>
<p>I'd like to discuss where we differ on the definition of
subsumption. I'm looking at your page on subsumption <a
class="moz-txt-link-freetext"
href="https://www.dprg.org/articles/2007-03a/">https://www.dprg.org/articles/2007-03a/</a>
since I don't have the books you are referencing. (Actually, I
found a PDF of "Mobile Robots" at
<a class="moz-txt-link-freetext"
href="https://cs.au.dk/~ocaprani/legolab/DigitalControl.dir/NXT/Lesson9.dir/11128_Mobile_Robots_Inspiration_to_Implementation-Flynn_and_Jones.pdf">https://cs.au.dk/~ocaprani/legolab/DigitalControl.dir/NXT/Lesson9.dir/11128_Mobile_Robots_Inspiration_to_Implementation-Flynn_and_Jones.pdf</a>"
<br>
</p>
<p> The book I started from was elementary and I disposed of it
during a recent move. I have read much on the web about
subsumption and BTs, and have implemented BTs for robotics work. <br>
</p>
<p>You refer to layers which I call behaviors. Rodney Brooks
original paper often conflated the two. <br>
</p>
<p>Looking at your section III. Arbitration you say:</p>
<blockquote>
<p>Subsumption tasks are arranged by priority, from lowest to
highest, as determined by the robot builder for a particular
problem set. An arbitrator() selects the output of the highest
priority task whose flag is true to pass on to the physical
subsystem (motors or whatever) for this pass through the loop,
this 20th of a second.<br>
<br>
Low priority tasks can only control the robot when all higher
priority tasks' flags are false.</p>
</blockquote>
<p>My description would be:</p>
<blockquote>
<p>Behaviors are listed in order of priority from highest to
lowest. Once the list is processed the highest priority task
that 'fires' is given control of the system. The default
behavior is the last on the list. <br>
</p>
</blockquote>
<p>Although my original reading of subsumption was that the entire
list was not processed but control passed once a behavior fired. I
modified this to process the entire list. Thus, my original
understanding may have been incorrect but I in inadvertently
changed to the correct processing. <br>
</p>
<p>You provide code from Flynn and Jones: <br>
</p>
<pre>void arbitrate()
{
while (1) {
if (cruise_output_flag == 1)
{motor_input = cruise_output; }
if (follow_output_flag == 1)
{motor_input = follow_output; }
if (avoid_output_flag == 1)
{motor_input = avoid_output; }
if (escape_output_flag == 1)
{motor_input = escape_output; }
sleep(tick);
}
}
</pre>
<p>I assert that this is an OR process with the caveat that the
default behavior always results in a true condition so it has
control. BTs are more complex having multiple lists to process so
a given set of behaviors (layer) is not likely to have a default
behavior. Subsumption is a <i>sequence</i> in a BT. From
<a class="moz-txt-link-freetext"
href="https://www.gamedeveloper.com/programming/behavior-trees-for-ai-how-they-work">https://www.gamedeveloper.com/programming/behavior-trees-for-ai-how-they-work</a><br>
</p>
<blockquote>
<p>Their main power comes from their ability to represent multiple
different courses of action, in order of priority from most
favorable to least favorable, and to return success if it
managed to succeed at any course of action. <br>
</p>
</blockquote>
<p>We may simply have a difference in terminology, as above, and
implementation details. <br>
</p>
<blockquote> </blockquote>
<div class="moz-signature"><font face="Comic Sans MS"
color="#000080"> <br>
-73 - <br>
<b>Rud Merriam K5RUD</b> <br>
<a href="http://mysticlakesoftware.com/"> <i>Mystic Lake
Software</i> </a> <br>
<br>
</font> </div>
<div class="moz-cite-prefix">On 10/28/21 8:35 AM, David P. Anderson
via DPRGlist wrote:<br>
</div>
<blockquote type="cite"
cite="mid:85af30b6-5045-9600-b756-bad65527cd9e@smu.edu">Howdy DPRG
<br>
<br>
On 10/27/21 10:23 PM, Rud Merriam via DPRGlist wrote: <br>
<br>
[snip] <br>
<blockquote type="cite"> <br>
If you're not familiar with subsumption is is a list of
behaviors or actions. Every cycle the list begins again until
one of the behaviors "fires". The processing starts again at the
beginning of the list. That's simplified but gives the idea. I
actually found that setting a flag and letting the list finish
processing also worked. Once the flag was any following behavior
would not "fire" but it could record information. That was
useful for handling behaviors that did a timing function. <br>
<br>
[snip] <br>
<br>
Subsumption is basically an OR operation, just like a logic
gate. If one behavior fires the overall gate becomes true and
returns to a higher level in the tree. There is also an AND
operation where all the behaviors must fire before returning
true. If one fails to fire a false is returned. The other main
operation is NOT which is an inverter of the output of a list. <br>
<br>
</blockquote>
If you're not familiar with subsumption, the above is not an
accurate description. At all. ;) <br>
<br>
For those who might be interested, the Joseph Jones books "Mobile
Robots" and "Behavior Based Robotics" provide sort of the
canonical definitions for subsumption and how it works. If you
don't want to read that much then I think I did a pretty good job
of describing it in the DPRG talk from last June, for which there
is a YouTube video on the club web page, (miss-labeled "May 12"
rather than "June 12"). <br>
<br>
cheers! <br>
<br>
David <br>
<br>
<br>
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<br>
</blockquote>
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