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## Re: [igraph] Extracting sub-graph

**From**: |
Tamás Nepusz |

**Subject**: |
Re: [igraph] Extracting sub-graph |

**Date**: |
Wed, 12 Oct 2011 15:09:36 +0200 |

>* decompose() seems to work for that purpose, but not on directed graphs.*
>* *
>* aa = i.decompose()*
>* igraph._igraph.InternalError: Error at components.c:463: only*
>* 'IGRAPH_WEAK' is implemented, Invalid value*
>* Note: unable to select mode='WEAK' with decompose(), is this a bug?*
Well, sort of. The decompose() method (or more precisely, the underlying
igraph_decompose function) has only been implemented to extract the weakly
connected components. However, I made two mistakes:
1) I have inadvertedly set the default value of the mode=... argument to
STRONG, which works for undirected graphs (since this argument is simply
ignored) but not for directed ones.
2) I have forgot to handle cases when the mode argument is specified as string.
So, this will work:
from igraph import Graph, WEAK
[...]
aa = i.decompose(mode=WEAK)
but this will not:
aa = i.decompose(mode="weak")
I'll fix this in the development version.
--
T.

**[igraph] Extracting sub-graph**, *Håvard Wahl Kongsgård*, `2011/10/12`
**Re: [igraph] Extracting sub-graph**, *Håvard Wahl Kongsgård*, `2011/10/12`
**Re: [igraph] Extracting sub-graph**,
*Tamás Nepusz* **<=**
**Re: [igraph] Extracting sub-graph**, *Håvard Wahl Kongsgård*, `2011/10/12`
**Re: [igraph] Extracting sub-graph**, *Tamás Nepusz*, `2011/10/12`
**Re: [igraph] Extracting sub-graph**, *Håvard Wahl Kongsgård*, `2011/10/12`
**Re: [igraph] Extracting sub-graph**, *Tamás Nepusz*, `2011/10/12`
**Re: [igraph] Extracting sub-graph**, *Håvard Wahl Kongsgård*, `2011/10/12`

**Re: [igraph] Extracting sub-graph**, *Tamás Nepusz*, `2011/10/12`