* An autonomous category
@ 2006-03-13 13:45 Marco Grandis
0 siblings, 0 replies; 2+ messages in thread
From: Marco Grandis @ 2006-03-13 13:45 UTC (permalink / raw)
To: categories
The Lawvere category of extended positive real numbers has also an
autonomous structure, with a multiplicative tensor product (instead
of the original additive one). Has this been considered somewhere?
To be more explicit:
The well-known article of Lawvere on "Metric spaces..." (Rend. Milano
1974, republished in TAC Reprints n. 1) introduced the category of
extended positive real numbers, from 0 to oo (infinity included),
with arrows x \geq y, equipped with a strict symmetric monoidal
closed structure: the tensor product is the sum, the internal hom is
truncated difference (with oo - oo = 0).
Now, the same category can be equipped with a multiplicative tensor
product, x.y.
Provided we define 0.oo = oo (so that tensoring by any element
preserves the initial object oo), this is again a strict symmetric
monoidal closed structure, with hom(y, z) = z/y. Now, the
'undetermined forms' 0/0 and oo/oo are defined to be 0.
The new multiplicative structure is even *-autonomous, with
involution x* = 1/x (and 'nearly' compact).
(Note that this choice of values of the undetermined forms comes from
privileging the direction x \geq y, which is necessary if we want
to view metric spaces, normed categories etc. as enriched categories).
Marco Grandis
^ permalink raw reply [flat|nested] 2+ messages in thread
* RE: An autonomous category
@ 2006-03-15 0:58 Stephen Lack
0 siblings, 0 replies; 2+ messages in thread
From: Stephen Lack @ 2006-03-15 0:58 UTC (permalink / raw)
To: categories
Dear Marco,
This has been considered by Brian Day. He spoke about it in a talk
*-autonomous convolution
in the Australian Category Seminar on 5 March 1999,
You can also transform this via the log/exponential functions to an
additive tensor product on the extended (positive and negative) reals.
Regards,
Steve Lack.
-----Original Message-----
From: cat-dist@mta.ca on behalf of Marco Grandis
Sent: Tue 14/03/2006 12:45 AM
To: categories@mta.ca
Subject: categories: An autonomous category
The Lawvere category of extended positive real numbers has also an
autonomous structure, with a multiplicative tensor product (instead
of the original additive one). Has this been considered somewhere?
To be more explicit:
The well-known article of Lawvere on "Metric spaces..." (Rend. Milano
1974, republished in TAC Reprints n. 1) introduced the category of
extended positive real numbers, from 0 to oo (infinity included),
with arrows x \geq y, equipped with a strict symmetric monoidal
closed structure: the tensor product is the sum, the internal hom is
truncated difference (with oo - oo = 0).
Now, the same category can be equipped with a multiplicative tensor
product, x.y.
Provided we define 0.oo = oo (so that tensoring by any element
preserves the initial object oo), this is again a strict symmetric
monoidal closed structure, with hom(y, z) = z/y. Now, the
'undetermined forms' 0/0 and oo/oo are defined to be 0.
The new multiplicative structure is even *-autonomous, with
involution x* = 1/x (and 'nearly' compact).
(Note that this choice of values of the undetermined forms comes from
privileging the direction x \geq y, which is necessary if we want
to view metric spaces, normed categories etc. as enriched categories).
Marco Grandis
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