Not signed in (Sign In)

Start a new discussion

Not signed in

Want to take part in these discussions? Sign in if you have an account, or apply for one below

  • Sign in using OpenID

Site Tag Cloud

2-categories 2-category 2-category-theory abelian-categories adjoint algebra algebraic algebraic-geometry algebraic-topology analysis analytic-geometry arithmetic arithmetic-geometry bundles calculus categories category category-theory chern-weil-theory cohesion cohesive-homotopy-theory cohesive-homotopy-type-theory cohomology colimits combinatorics complex-geometry computable-mathematics computer-science connection constructive constructive-mathematics cosmology definitions deformation-theory descent diagrams differential differential-cohomology differential-equations differential-geometry differential-topology digraphs duality elliptic-cohomology enriched fibration finite foundations functional-analysis functor galois-theory gauge-theory gebra geometric-quantization geometry goodwillie-calculus graph graphs gravity grothendieck group-theory harmonic-analysis higher higher-algebra higher-category-theory higher-differential-geometry higher-geometry higher-lie-theory higher-topos-theory history homological homological-algebra homotopy homotopy-theory homotopy-type-theory index-theory integration integration-theory internal-categories k-theory lie-theory limit limits linear linear-algebra locale localization logic mathematics measure-theory modal-logic model model-category-theory monoidal monoidal-category-theory morphism motives motivic-cohomology multicategories noncommutative noncommutative-geometry number-theory of operads operator operator-algebra order-theory pasting philosophy physics pro-object probability probability-theory quantization quantum quantum-field quantum-field-theory quantum-mechanics quantum-physics quantum-theory question representation representation-theory riemannian-geometry scheme schemes set set-theory sheaf simplicial space spin-geometry stable-homotopy-theory stack string-theory superalgebra supergeometry svg symplectic-geometry synthetic-differential-geometry terminology theory topological topology topos topos-theory type type-theory universal variational-calculus

Vanilla 1.1.10 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to nForum
If you want to take part in these discussions either sign in now (if you have an account), apply for one now (if you don't).
    • CommentRowNumber1.
    • CommentAuthorUrs
    • CommentTimeMar 25th 2010
    • (edited Mar 25th 2010)

    added to simplicial model category a handful of theorems that state when and how a model category is Quillen equivalent to a simplicial model category.

    My motivation for filling this in was actually that I was reading van den Berg/Garner types are weak omega-groupoids and my impression was that the main theorem there is morally the usual simplicial resolution technique in model categories, only that instead of simplicial objects they use globular objects.

    The other main statement in there I hope we can isolate in some other entry (and it may go back to other authors?): that the context categories of certain type theoreies with identity types naturally carry the structure of somthing close to a category with fibrant objects.

    • CommentRowNumber2.
    • CommentAuthorUrs
    • CommentTimeMar 25th 2010

    noticed that a bit of information was missing and somewhat hastily added some in at simplicial model category: a section on Properties, a warning on terminology, a section on combinatorial simplicial model categories.

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeNov 10th 2011

    Expanded the Properties-section at simplicial model category by more discussion of Enrichment, tensoring, and cotensoring

    • CommentRowNumber4.
    • CommentAuthorUrs
    • CommentTimeApr 15th 2012
    • (edited Apr 15th 2012)

    I am trying to brush-up and expand simplicial model category for a seminar talk.

    There is a uniqueness theorem for model structures on simplicial objects cited here, being theorem 3.1 in the article by Rezk-Schwede-Shipley mentioned there. Am I missing something: isn’t this uniqueness a trivial consequence of the fact that model structures are determined by their cofibrations and fibrant objects? Is the observation of that general fact younger than that theorem?

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeApr 16th 2012

    okay, I have added more details in the section Simplicial Quillen equivalent model structures.

    • CommentRowNumber6.
    • CommentAuthorMike Shulman
    • CommentTimeApr 16th 2012

    I would speculate that you are correct, i.e. that the general fact (due I think to Joyal?) was not known to RSS at the time of writing that paper.

    • CommentRowNumber7.
    • CommentAuthorUrs
    • CommentTimeApr 16th 2012

    that the general fact (due I think to Joyal?)

    At least I know it from his notes on quasi-categories.

    was not known to RSS at the time of writing that paper.

    Okay, I see. Seems to be kind of surprising, given that it is a simple elementary argument. But then, that’s how it goes.

    • CommentRowNumber8.
    • CommentAuthorMike Shulman
    • CommentTimeApr 16th 2012

    The fact surprised me a bit when I heard it. It’s obvious from the definition of model category that any two of the three classes of maps determine the third, and after you get used to that idea it may also seem “obvious” that just knowing the fibrant objects probably wouldn’t be enough, that you’d need to know all the fibrations. Of course what’s surprising to one person may be obvious to another. (-:

    • CommentRowNumber9.
    • CommentAuthorUrs
    • CommentTimeApr 16th 2012
    • (edited Apr 16th 2012)

    With the fact in hand, it’s hard to imagine how hard it is to guess it. But at least phrasing the proof in words as follows makes it seem non-surprising and non-mysterious:

    “Given the cofibrations, fibrant objects are sufficient for computing derived homs into fixed objects, and these in turn are sufficient for determining the weak equivalences.”

    Of course the answer to every riddle is obvious once one has it. But at least this one seems to be straightforward and not involve any tricks.

    • CommentRowNumber10.
    • CommentAuthorUrs
    • CommentTimeApr 16th 2012

    I have added the proof of three of the items in the big theorem in the section on resolutions by simplicial model structures.

    Will have to quit now, hope to further expand and polish tomorrow.

    • CommentRowNumber11.
    • CommentAuthorUrs
    • CommentTimeApr 18th 2012
    • (edited Apr 18th 2012)

    I have written out here essentially all of the proof of

    • Dugger, Replacing model categories with simplicial ones (web)

    on how a model category may be replaced by a Quillen equivalent simplicial one.

    I am feeling a bit dumb, but there is one step which seems to have a gap to me:

    in theorem 5.2 b) the claim is that the usual Quillen adjunction (colimconst):C[Δ op,C] proj(colim \dashv const) : C \to [\Delta^{op}, C]_{proj} descends to the localization of [Δ op,C] proj[\Delta^{op}, C]_{proj} that makes it have as weak equivalences the maps that become weakly equivalent under hocolim.

    It says in the proof: “constconst clearly preserves fibrations and trivial fibrations”. Is this clear? For the unlocalized structure of course, but for the local structure?. What is clear from item c) of the same theorem is that const:C[Δ op,C] proj,localizedconst : C \to [\Delta^{op}, C]_{proj,localized} preserves fibrant objects, and from a) that it preserves weak equivalences. But fibrations?

    • CommentRowNumber12.
    • CommentAuthorMike Shulman
    • CommentTimeApr 23rd 2012

    Perhaps one needs to insert a reference to Hirschhorn, 3.3.18? If an adjunction MNM\rightleftarrows N is Quillen and we localize MM at some class of maps whose derived images become weak equivalences in NN, then we still have a Quillen adjunction.

    • CommentRowNumber13.
    • CommentAuthorUrs
    • CommentTimeApr 23rd 2012

    Ah, thanks Mike. I was missing that. I was actively aware of the similar statement for simplicial left proper model categories which is currently prop. 4 at Quillen equivalence. This would imply this result… were it not for the fact that in the present context simplicialness is the very thing to be shown.

    Okay, thanks, so I added that prop. 3.3.18 at Quillen adjunction- behaviour under localization and have patched the discussion at simplicial model category with a pointer to this.

    • CommentRowNumber14.
    • CommentAuthorMike Shulman
    • CommentTimeApr 23rd 2012

    3.3.18 makes use of a statement (8.5.4) similar to Prop. 4, that for a right adjoint to be a right Quillen functor it suffices for it to preserve (1) acyclic fibrations and (2) fibrations between fibrant objects. I haven’t looked at the proofs of either, but is there any chance that Prop. 4 only uses the simplicial structure as a crutch and would work just as well in the non-simplicial case?

    Prop. 3 at Quillen adjunction also seems to me like it really shouldn’t depend on the model categories being simplicial.

    • CommentRowNumber15.
    • CommentAuthorUrs
    • CommentTimeApr 23rd 2012

    That could well be, yes. I should go through all these statements and generalize them where possible.

    • CommentRowNumber16.
    • CommentAuthorMike Shulman
    • CommentTimeDec 31st 2018

    Added the proposition that simplicial homotopy equivalences are weak equivalences.

    diff, v34, current

Add your comments
  • Please log in or leave your comment as a "guest post". If commenting as a "guest", please include your name in the message as a courtesy. Note: only certain categories allow guest posts.
  • To produce a hyperlink to an nLab entry, simply put double square brackets around its name, e.g. [[category]]. To use (La)TeX mathematics in your post, make sure Markdown+Itex is selected below and put your mathematics between dollar signs as usual. Only a subset of the usual TeX math commands are accepted: see here for a list.

  • (Help)