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<p>Hi Rud,</p>
<p>Ok, that sounds good to me. Different descriptions of basically
the same thing. I'd be more inclined to emphasize the "subsume"
nature of subsumption and it's ramifications, which are pretty
deep once you scratch the surface.</p>
<p>cheers!</p>
<p>David</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 10/28/21 1:13 PM, Rud Merriam via
DPRGlist wrote:<br>
</div>
<blockquote type="cite"
cite="mid:e0402033-8ce9-6e46-c8b1-d6f82aaca113@gmail.com">
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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/"
moz-do-not-send="true">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"
moz-do-not-send="true">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://secure-web.cisco.com/1HXrCYXElnauuP1wfG6OxvXrlL-J-d3OrUFTMKM96QobUddG2ojoZCrHp-ZZNkzoJhYQ4tvpZZ36MdJQnmpEBLTXCN3RWyvl20Si2uOnbizEobwRRwcIMLZl8CJPVEblm7PtbjZW6-u9hegWLaYbsqkMSXlGH2gaVSHmQhzSOxEJ7TR7FmX1lZMFWjAMQFWB209jGfKezZPIFR3JQN5C-WeoUGYuWPT3yHWP2K46iyAXfRnW7XKXeUOMyX_7YlKEDgnDaOgnt7mcdk6dyQhd6NxW9FiK6DySJ95Lb866o1Jw/https%3A%2F%2Fwww.gamedeveloper.com%2Fprogramming%2Fbehavior-trees-for-ai-how-they-work"
moz-do-not-send="true">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://secure-web.cisco.com/1FKz_X0Ge1ie37k5LHDucUXiDVc-D1xvohLqcTDESE8BjeMVz7ksqQwfV3iUyqpDovtR-0-tn_yo8xt3L2xqvqvv1McOdn6AJOJQ-sFHYPgpnyZbMrjcS1zL51KTf7SbGRDPmH40a1teuLnvGDFDeNOk23sIq4YNsSUIGc-VZkskk0UV7LZfvdcOt95nBziNnV4YwBopI_dF6oloKbUyhiVLmT4A_2qMkmYYIVGNbo_menDPskLCcvqr7VqB-Q-sN4obSw-KecZ1m1TTzyy0Hz9W-oraDa2B2qGphSnHGPY4/http%3A%2F%2Fmysticlakesoftware.com%2F"
moz-do-not-send="true"> <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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