The VRPLIB format

PyVRP supports reading benchmark instances in the VRPLIB format through the VRPLIB package. Although generally used, this format is not all that well standardised, so it merits some description what PyVRP actually supports. In addition to standard specifications and data sections, PyVRP uses several data sections that are not commonly found in (other) benchmark instances. On this page, we explain all specifications and data sections that PyVRP understands.

This page can be useful in understanding how benchmark instances should be formatted to work with PyVRP’s read() function. All instances in our instances repository adhere to this format, and use the specifications and data sections described below.

Note

Any specification or data section in a VRPLIB-formatted file that is not defined in the glossaries below is not understood by PyVRP, and will be silently ignored.

Specifications

Specifications are key-value pairs. PyVRP supports the following specifications:

CAPACITY

Homogeneous capacity of all vehicles in the instance. To specify heterogeneous capacities, see CAPACITY_SECTION.

DIMENSION

Number of locations in the instance. This is the sum of the number of depots and the number of clients.

EDGE_WEIGHT_FORMAT

Specifies the format of the EDGE_WEIGHT_SECTION if the edge weights are given explicitly.

EDGE_WEIGHT_TYPE

Specifies how the edge weights (distances and durations) are given.

SERVICE_TIME

Service time for all clients. To specify heterogeneous client service times, see SERVICE_TIME_SECTION.

VEHICLES

Number of vehicles in the instance. The number of vehicles defaults to the number of clients in the instance when this specification is not provided: PyVRP assumes an unlimited fleet in this case.

VEHICLES_MAX_DISTANCE

Maximum route distance for all vehicles. To specify heterogeneous maximum route distances, see VEHICLES_MAX_DISTANCE_SECTION.

VEHICLES_MAX_DURATION

Maximum route duration for all vehicles. To specify heterogeneous maximum route durations, see VEHICLES_MAX_DURATION_SECTION.

Data sections

Data sections are array-like values that specify the actual problem data. PyVRP supports the following data sections:

BACKHAUL_SECTION

Array of backhaul quantities, one for each location. This is the amount picked up at the client and transported back to the depot.

CAPACITY_SECTION

Capacity for each vehicle, typically used in heterogeneous fleet instances. Vehicle capacities are assumed to be unconstrained if this section is not present.

DEMAND_SECTION
LINEHAUL_SECTION

Array of demands, one for each location. This is the delivery amount from the depot to the client.

DEPOT_SECTION

Array of location indices that are depots. These location indices should be the contiguous lower indices, starting from 1.

EDGE_WEIGHT_SECTION

When provided, this section explicitly describes the distance and duration matrices. If not provided, such matrices are computed based on what’s specified for EDGE_WEIGHT_FORMAT and EDGE_WEIGHT_TYPE.

MUTUALLY_EXCLUSIVE_GROUP_SECTION

When provided, this section describes client memberships of mutually exclusive groups. Of all clients in such a group, exactly one must be visited.

NODE_COORD_SECTION

Array of \((x, y)\) coordinates for each location.

PRIZE_SECTION

Array of prizes for visiting each location. A value of zero for non-depots implies visiting that location is required.

RELEASE_TIME_SECTION

Array of release times for each location.

SERVICE_TIME_SECTION

Array of service durations for each location.

TIME_WINDOW_SECTION

Array of \([e, l]\) time window data, for each location.

VEHICLES_ALLOWED_CLIENTS_SECTION

Lists specifying the client locations that each vehicle is allowed to service, one list for each vehicle. Each vehicle is allowed to visit each client if this section is not provided. This section is commonly used in site-dependent instances.

VEHICLES_DEPOT_SECTION

Depot assignments for each vehicle, typically used in multi-depot instances. Vehicles are assigned to the first depot if this section is not provided.

VEHICLES_MAX_DISTANCE_SECTION

Maximum route distance for each vehicle. Route distances are assumed to be unconstrained if this section is not present.

VEHICLES_MAX_DURATION_SECTION

Maximum route duration for each vehicle. Route durations are assumed to be unconstrained if this section is not present.