[pgrouting-dev] Re: Implementation of core Time Dependent Dijkstra function

[Stephen Woodbridge]

When I was looking at this code I had the similar thoughts regarding 
boost_dijkstra(). In fact in my mind I would replace both directed and 
has_reverse_cost with one variable "char *reverse_cost". if this is null 
then the graph is undirected. if this has a value then it is the column 
name of the reverse cost column and it is directed.

Or alternatively, if the reverse cost column name is always 
"reverse_cost" then you only need has_reverse_cost and the fact that 
this is set implies a directed graph.

Seems like Anton has come to the same conclusion also. I'm not sure if 
there is any value building a directed graph when reverse_cost=cost.

-Steve

On 6/6/2011 2:24 AM, Anton Patrushev wrote:
> Hi Jay,
>
> Those two parameters exist mostly by historical reasons (hysterical raisins :))
> Of course indirected graph can be represented by directed graph where
> reverse costs for all edges are equal to costs. But in this case we
> need one extra non-empty field in edges table which increases the
> amount of stored data (not big deal though).
>
> Now if undirected = true, we add reverse_cost=cost automatically.
>
> In your case I guess that graph is directed without reverse cost.
>
> Anton.
>
> On 6/6/11, Jay Mahadeokar<jai.mahadeokar at gmail.com>  wrote:
>> Hi,
>>
>> I am writing a function tdsp_caller() which will call the core tdsp()
>> function, on lines of boost_dijkstra() function in boost_wrapper.cpp.
>>
>> The prototype is like this:
>> int tdsp_wrapper(
>>
>>              edge_columns_t *edges,
>>              unsigned int edge_count,
>>              weight_map_element_t *weight_map_elements,
>>              int weight_map_element_count,
>>              int start_vertex,
>>              int end_vertex,
>>              bool directed,
>>              bool has_reverse_cost,
>>              path_element_t **path,
>>              int *path_count,
>>              char **err_msg
>>
>>              );
>>
>> I am confused about the has_reverse_cost and directed variables in this
>> scenario. I have mainly tested for directed graphs till now. I think for
>> undirected graphs, we can add reverse edge while generating graph to make it
>> directed.
>>
>> Now, since the costs here are the travel_time in the weight_map
>> corresponding to each start_time, do we need a has_reverse_cost variable
>> here? If yes, what would be its significance?
>>
>> Regards,
>>
>> --
>> Regards,
>> -Jay Mahadeokar
>>
>
>