# pgRouting Manual (2.1.0)

## pgr_vidsToDMatrix

## Name

`pgr_vidsToDMatrix` - Creates a distances matrix from an array of `vertex_id`.

## Synopsis

This function takes an array of `vertex_id`, a `sql` statement to select the edges, and some boolean arguments to control the behavior. It then computes kdijkstra() distances for each vertex to all the other vertices and creates a distance matrix suitable for TSP.

The function returns:

> - dmatrix: | `float8[]` - the distance matrix suitable to pass to pgr_TSP() function.

    pgr_vidsToDMatrix(IN sql text, IN vids integer[], IN directed boolean, IN has_reverse_cost boolean, IN want_symmetric boolean, OUT dmatrix double precision[])

## Description

Paramters

sql: | `text` - A SQL statement to select the edges needed for the solution.
vids: | `integer[]` - An array of `vertex_id`.
directed: | `boolean` - A flag to indicate if the graph is directed.
has_reverse_cost:
| `boolean` - A flag to indicate if the SQL has a column `reverse_cost`.
want_symmetric: | `boolean` - A flag to indicate if you want a symmetric or asymmetric matrix. You will need a symmetric matrix for pgr_TSP(). If the matriix is asymmetric, the then the cell(i,j) and cell(j,i) will be set to the average of those two cells except if one or the other are -1.0 then it will take the value of the other cell. If both are negative they will be left alone.

Warning

- kdijkstra() can fail to find a path between some of the vertex ids. We to not detect this other than the cost might get set to -1.0, so the dmatrix shoule be checked for this as it makes it invalid for TSP

History

- New in version 2.1.0

## Examples

This example shows how this can be used in the context of feeding the results into pgr_tsp() function. We convert a text string of `x,y;x,y;...` into and array of points, then convert that into an array `vertex_id`, then create a distance matrix that gets feed into `pgr_tsp()` that returns the final result.

    select * from pgr_tsp(
        (select dmatrix::float8[]
           from pgr_vidstodmatrix(
                    'select id, source, target, cost, reverse_cost from edge_table',
                    pgr_pointstovids(
                        pgr_texttopoints('2,0;2,1;3,1;2,2;4,1;4,2;2,3;3,2', 0),
                        'edge_table'),
                    true, true, true) as dmatrix
        ),
        1
    );
     seq | id
    -----+----
       0 |  1
       1 |  0
       2 |  6
       3 |  3
       4 |  7
       5 |  5
       6 |  4
       7 |  2
    (8 rows)

This example uses the Sample Data network.

## See Also

- pgr_vidsToDMatrix - - Creates a distances matrix from an array of `vertex_id`.
- pgr_textToPoints - Create an array of points from a text string.
- pgr_tsp - Traveling Sales Person