| dm.ddf | R Documentation | 
Implements Chambers' directional distance function (non-radial & non-oriented measure).
dm.ddf(xdata, ydata, rts="crs", g=NULL, 
       wd=NULL, se=FALSE, sg="ssm", date=NULL, cv="convex", o=NULL)| xdata | Input(s) vector (n by m) | 
| ydata | Output(s) vector (n by s) | 
| rts | Returns to scale assumption  | 
| g | Directional vector indicating a measurement direction (n by (m+s)) | 
| wd | Weak disposability vector indicating (an) undesirable output(s) (1 by s) | 
| se | Implements super-efficiency model alike Anderson & Peterson's model if  | 
| sg | Employs second-stage optimization  | 
| date | Production date (n by 1) | 
| cv | Convexity assumption  | 
| o | DMU index to calc.  | 
| $eff | Efficiency score | 
| $lambda | Intensity vector | 
| $mu | Secondary intensity vector for weak disposability under VRS | 
| $beta | Input reduction factor | 
| $gamma | Output augmentation factor | 
| $xslack | Input slack | 
| $yslack | Output slack | 
Dong-Joon Lim, PhD
Chambers, Robert G., Yangho Chung, and Rolf Fare. "Profit, directional distance functions, and Nerlovian efficiency." Journal of optimization theory and applications 98.2 (1998): 351~364.
Fare, Rolf, and Shawna Grosskopf. "Directional distance functions and slacks-based measures of efficiency." European journal of operational research 200.1 (2010): 320~322.
dm.ddf Distance measure using DDF 
dm.dea Distance measure using DEA 
dm.hdf Distance measure using HDF 
dm.sbm Distance measure using SBM 
dm.sf Distance measure using SF
# Additive form directional distance function
  # ready
  x <- matrix(c(5, 1, 4), ncol = 1)
  y <- matrix(c(8, 3, 5, 6, 4, 1), ncol = 2)
  g <- matrix(c(1), nrow = 3, ncol = 3) 
  w <- matrix(c(1, 0), ncol = 2)
  # go
  dm.ddf(x, y, "crs", g, w)
# Multiplicative form directional distance function
  # ready
  g <- cbind(x, y)
  # go
  dm.ddf(x, y, "crs", g, w)
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