Definition of subroutines

We now show a package (file solarraypkg.mos) that defines several versions of a subroutine, solarray, which copies the solution values of an array of decision variables of type mpvar into an array of real of the same size. For each desired number (1–3) and type (integer or string) of array indices we need to define a new version of this subroutine.

package solarraypkg

! **** Integer indices (including ranges) ****
 public procedure solarray(x:array(R:set of integer) of mpvar,
                           s:array(set of integer) of real)
  forall(i in R) s(i):=getsol(x(i))
 end-procedure

 public procedure solarray(x:array(R1:set of integer,
                                   R2:set of integer) of mpvar,
                           s:array(set of integer,
                                   set of integer) of real)
  forall(i in R1, j in R2) s(i,j):=getsol(x(i,j))
 end-procedure

 public procedure solarray(x:array(R1:set of integer,
                                   R2:set of integer,
                                   R3:set of integer) of mpvar,
                           s:array(set of integer,
                                   set of integer,
                                   set of integer) of real)
  forall(i in R1, j in R2, k in R3) s(i,j,k):=getsol(x(i,j,k))
 end-procedure

! ****String indices ****
 public procedure solarray(x:array(R:set of string) of mpvar,
                           s:array(set of string) of real)
  forall(i in R) s(i):=getsol(x(i))
 end-procedure

 public procedure solarray(x:array(R1:set of string,
                                   R2:set of string) of mpvar,
                           s:array(set of string,
                                   set of string) of real)
  forall(i in R1, j in R2) s(i,j):=getsol(x(i,j))
 end-procedure

 public procedure solarray(x:array(R1:set of string,
                                   R2:set of string,
                                   R3:set of string) of mpvar,
                           s:array(set of string,
                                   set of string,
                                   set of string) of real)
  forall(i in R1, j in R2, k in R3) s(i,j,k):=getsol(x(i,j,k))
 end-procedure
end-package

Using the package in a Mosel model (file solarr_test.mos):

model "Test solarray package"
 uses "solarraypkg", "mmxprs"

 declarations
  R1=1..2
  R2={6,7,9}
  R3={5,-1}
  x: array(R1,R2,R3) of mpvar
  sol: array(R1,R2,R3) of real
 end-declarations

! Define and solve a small problem
 sum(i in R1, j in R2, k in R3) (i+j+2*k) * x(i,j,k) <= 20
 forall(i in R1, j in R2, k in R3) x(i,j,k)<=1
 maximize(sum(i in R1, j in R2, k in R3) (i+2*j+k) * x(i,j,k))

! Get the solution array
 solarray(x,sol)

! Print the solution
 forall(i in R1, j in R2, k in R3)
  writeln(" (", i, ",", j, ",", k, ") ", sol(i,j,k), " ", getsol(x(i,j,k)))
 writeln(sol)

end-model

Output produced by this model:

 (1,6,-1) 1 1
 (1,6,5) 0 0
 (1,7,-1) 1 1
 (1,7,5) 0 0
 (1,9,-1) 1 1
 (1,9,5) 0 0
 (2,6,-1) 0.166667 0.166667
 (2,6,5) 0 0
 (2,7,-1) 0 0
 (2,7,5) 0 0
 (2,9,-1) 0 0
 (2,9,5) 0 0
[1,0,1,0,1,0,0.166667,0,0,0,0,0] 

This example may be classified as a `utility function' that eases tasks occurring in a similar way in several of your models. Another example of such a utility function could be a printing function that simply outputs the solution value of a decision variable with some fixed format (if you apply write/writeln to a decision variable of type mpvar you obtain the pointer of the variable, and not its solution value).

If we again make the comparison with the implementation as a module we see that both ways have their positive and negative points: the implementation as a module is clearly more technical, requiring a considerable amount of C code not immediately related to the implementation of the function itself. However, at the C level we simply check that the two arguments have the same index sets, without having to provide a separate implementation for every case, thus making the definition more general.