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Reading input file line by line in Xpress
Reading input file line by line in Xpress
I am trying to iteratively solve a given model as followsforall(c in 1..|C|) do
min_x {c'x | A(c)x=b}
end-do
where A(c) is a single line of the matrix A. Matriz A can be huge and I have found out that just by loading it, the entire solving process is slowed down considerably. So what I am trying to do is instead of initializing the whole matrix, I am trying to read line by line and solving the model with it.
I have tried using fopen and read/readln commands but without any success.
Any thoughts?
Thank you very much
2 Replies
Here is a small example how to combine linewise reading with constraint redefinition (for simplicity's sake all data are contained in the model, to read some text data file you just need to remove the "text:" I/O driver prefix in the file name in "fopen"). I am assuming dense data for the coefficient matrix A - if this is not the case, you could define A as "dynamic array" and add delcell(A) before reading in a new line of data, and adapt the reading to sparse-format (that is, index+value) data.
model "test linewise read"
uses "mmxprs" uses "mmsystem"declarations
I=1..5 Ctrs=1..3 x: array(I) of mpvar A: array(I) of real B: array(Ctrs) of real C: array(I) of real public testdata: text end-declarations! Some test data (usually read from file)
C::(1..5)[1,2,3,4,5] B::(1..3)[10,51,92]testdata:=
` 1 2 3 4 5 11 12 13 14 15 21 22 23 24 25 `! Invariable portion of the problem definition
Obj:=sum(i in I) C(i)*x(i) forall(i in I) x(i) is_integerct:=0
fopen("text:testdata",F_INPUT) while (not iseof) do forall(i in I) read(A(i)) readln ct+=1 ! Redefine the constraint at every iteration Ctr:=sum(i in I) A(i)*x(i) = B(ct) minimize(Obj) if getprobstat=XPRS_OPT then writeln("Solution: ", getobjval) forall(i in I) write(" ", i, ":", x(i).sol) writeln else writeln("No solution") end-if end-do fclose(F_INPUT)end-model
Thank you very much! Exactly what I was looking for.
