[R] Add transitivity to a matrix?
Duncan Murdoch
murdoch@dunc@n @end|ng |rom gm@||@com
Tue Jun 18 02:08:15 CEST 2019
On 17/06/2019 7:34 p.m., Bert Gunter wrote:
> Depends on what you mean by "simple" of course, but suppose that:
>
> M[i,j] & M[j,k] & M[k,n] are TRUE and M[i,k] and M[i,n] are FALSE.
> Then the procedure would see that M[i,k] needs to change to TRUE, but
> not that M[i,n] needs to also become TRUE *after* M[i,k] changes. This
> seems to imply that an iterative solution is necessary.
Right, that's a good point.
Duncan Murdoch
>
> One such procedure, via repeated matrix multiplication to check for and
> impose transitivity, appears to be suggested by this discussion:
> https://math.stackexchange.com/questions/228898/how-to-check-whether-a-relation-is-transitive-from-the-matrix-representation
>
> Cheers,
> Bert
>
>
>
> On Mon, Jun 17, 2019 at 10:29 AM Duncan Murdoch
> <murdoch.duncan using gmail.com <mailto:murdoch.duncan using gmail.com>> wrote:
>
> On 17/06/2019 1:19 p.m., Duncan Murdoch wrote:
> > Suppose I have a square logical matrix M which I'm thinking of as a
> > relation between the row/column numbers.
> >
> > I can make it into a symmetric relation (i.e. M[i,j] being TRUE
> implies
> > M[j,i] is TRUE) by the calculation
> >
> > M <- M | t(M)
> >
> > Is there a simple way to ensure transitivity, i.e. M[i,j] &
> M[j,k] both
> > being TRUE implies M[i,k] is TRUE?
> >
> > The operation should only change FALSE or NA values to TRUE
> values; TRUE
> > values should never be changed.
>
> I also want the changes to be minimal; changing everything to TRUE
> would
> satisfy transitivity, but isn't useful to me.
>
> Duncan Murdoch
>
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