For the project I'm working on I need to calculate distances on a graph
from a couple of vertices to all other vertices. The
topology.shortest_distance can only do either from all vertices or from a
single one, and to save time I'd like this to run in parallel, so I set out
to implement this in C++. I took inspiration from graph-tool's
implementation of shortest_distance for pair-wise distances in unweighted
graphs (running BFS from all vertices in parallel), and managed to modify
that to only run from some vertices. However I ran into a problem trying to
do the same for weighted graphs. I think the problem I have is that when
passing the vector for distances to all vertices it is supposed to be a
property map and not a vector, but I cannot figure out how to get a 1d
property map from a 2d property map on a C++ level, basically I pass a
vector<double> property map to my function but I need to pass a simple
double property map to the dijskstra function from boost. Could anyone
please help me point to how would I do that? Or is my approach wrong
completely? What most confuses me that the same approach works fine for
breadth_first_search.
The errors I'm getting in compilation:
/usr/include/boost/graph/dijkstra_shortest_paths_no_color_map.hpp:43:63:
error: no type named ‘value_type’ in ‘struct
boost::property_traits<std::vector<double> >’
43 | typedef typename property_traits<DistanceMap>::value_type
Distance;
/usr/include/boost/pending/indirect_cmp.hpp:32:78: error: no type named
‘value_type’ in ‘struct boost::property_traits<std::vector<double> >’
32 | typedef typename
boost::property_traits<ReadablePropertyMap>::value_type T;
>
^
/usr/include/boost/pending/indirect_cmp.hpp:33:76: error: no type named
‘key_type’ in ‘struct boost::property_traits<std::vector<double> >’
33 | typedef typename
boost::property_traits<ReadablePropertyMap>::key_type K;
Posting the compilation errors without showing the source code is not
very useful...
It's possible to adapt property maps, but I think the simplest approach
for you would be to use an auxiliary scalar property map, and then copy
its values into the vector property map. However, I'm only speculating,
since you described your task only very vaguely.
In that example, ss is a list of property maps, as the code shows. Each
item in the list contains a property map with the state of all nodes for
one point in time. So, e.g. ss[10][v] refers to the state of node 'v' at
time 10.
Thanks, but I'm still a bit confused as ss[10][v] is an array of length 10,
does it mean that the whole vector represents a single state for v? And when
I try to copy other time series in ss
sss=[]
for i in range(200):
vpp=gp.new_vp("vector<double>")
for v in gp.get_vertices():
x = np.array(ts[i])[0][v]
vpp[v]=np.array([x])
sss.append(vpp)
Ah, sorry it is fact transposed. In the original example, ss is a list
of many time series. Each one is a vector-value property map, containing
for each node its own time series.
(BTW, please don't post images of error messages which are just text.
Just post the text.)
