[R] Add transitivity to a matrix?

[Duncan Murdoch]

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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