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Read and write TSPLIB files

Source: R/TSPLIB.R
TSPLIB.Rd

Reads and writes TSPLIB format files. TSPLIB files can be used by most TSP solvers. Many problems in TSPLIB format can be found in the local copy of the TSPLIB95 problem library.

Usage

read_TSPLIB(file, precision = 0)

write_TSPLIB(x, file, precision = 6, inf = NULL, neg_inf = NULL)

# S3 method for class 'TSP'
write_TSPLIB(x, file, precision = 6, inf = NULL, neg_inf = NULL)

# S3 method for class 'ATSP'
write_TSPLIB(x, file, precision = 6, inf = NULL, neg_inf = NULL)

# S3 method for class 'ETSP'
write_TSPLIB(x, file, precision = 6, inf = NULL, neg_inf = NULL)

Arguments

file

file name or a connection.

precision

controls the number of decimal places used to represent distances (see details). If x already is integer, this argument is ignored and x is used as is.

x

an object with a TSP problem. NAs are not allowed.

inf

replacement value for Inf (TSPLIB format cannot handle Inf). If inf is NULL, a large value of \(max(x) + 2 range(x)\) (ignoring infinite entries) is used.

neg_inf

replacement value for -Inf. If no value is specified, a small value of \(min(x) - 2 range(x)\) (ignoring infinite entries) is used.

Value

returns an object of class TSP or ATSP.

Details

In the TSPLIB format distances are represented by integer values. Therefore, if x contains double values (which is normal in R) the values given in x are multiplied by \(10^{precision}\) before coercion to integer. Note that therefore all results produced by programs using the TSPLIB file as input need to be divided by \(10^{precision}\) (i.e., the decimal point has to be shifted precision places to the left).

Currently only the following EDGE_WEIGHT_TYPEs are implemented: EXPLICIT, EUC_2D, EUC_3D, ATT and GEO.

References

Reinelt, Gerhard. 1991. “TSPLIB—a Traveling Salesman Problem Library.” ORSA Journal on Computing 3 (4): 376–84. doi:10.1287/ijoc.3.4.376

See also

Other data: USCA

Author

Michael Hahsler

Examples


## Drilling problem from TSP
drill <- read_TSPLIB(system.file("examples/d493.tsp", package = "TSP"))
drill
#> object of class ‘ETSP’ 
#> 493 cities (Euclidean TSP)
tour <- solve_TSP(drill, method = "nn", two_opt = TRUE)
tour
#> object of class ‘TOUR’ 
#> result of method ‘nn+two_opt’ for 493 cities
#> tour length: 37870.05 
plot(drill, tour, cex=.6, col = "red", pch= 3, main = "TSPLIB: d493")



## Write and read data in TSPLIB format
x <- data.frame(x=runif(5), y=runif(5))

## create TSP, ATSP and ETSP (2D)
tsp <- TSP(dist(x))
atsp <- ATSP(dist(x))
etsp <- ETSP(x[,1:2])

write_TSPLIB(tsp, file="example.tsp")
#file.show("example.tsp")
r <- read_TSPLIB("example.tsp")
r
#> object of class ‘TSP’ 
#> 5 cities (distance ‘unknown’) 

write_TSPLIB(atsp, file="example.tsp")
#file.show("example.tsp")
r <- read_TSPLIB("example.tsp")
r
#> object of class ‘ATSP’  (asymmetric TSP) 
#> 5 cities (distance ‘unknown’) 

write_TSPLIB(etsp, file="example.tsp")
#file.show("example.tsp")
r <- read_TSPLIB("example.tsp")
r
#> object of class ‘ETSP’ 
#> 5 cities (Euclidean TSP)

## clean up
unlink("example.tsp")