Question

我一直在经历glpsol的奇怪行为，更确切地说是其中一个变量。我使用glpsol -m sol.mod

运行命令

输入，在文件sol.mod中：

set Points := (1..3);
var a{i in Points}, >= 0;
var x1{i in Points};
var x2{i in Points};
maximize obj: sum{i in Points} a[i];
px1: x1[1] = 0;
py1: x2[1] = 0;
px2: x1[2] = 2;
py2: x2[2] = 1;
px3: x1[3] = 3;
py3: x2[3] = 3;
p1x2: x1[1] + a[1] <= x1[2] - a[2];
p1x3: x1[1] + a[1] <= x1[3] - a[3];
p2x3: x2[2] + a[2] <= x2[3] - a[3];
solve;
printf "#OUTPUT:\n";
#printf{i in Points} "a_%d = %d\n", i, a[i];
printf "a[1]: %d\n", a[1];
printf "-a[1]: %d\n", -a[1];
printf "a[3]: %d\n", a[3];
printf "#OUTPUT END:\n";
end;

输出：

    GLPSOL: GLPK LP/MIP Solver, v4.52
Parameter(s) specified in the command line:
 -m sol.mod
Reading model section from sol.mod...
22 lines were read
Generating obj...
Generating px1...
Generating py1...
Generating px2...
Generating py2...
Generating px3...
Generating py3...
Generating p1x2...
Generating p1x3...
Generating p2x3...
Model has been successfully generated
GLPK Simplex Optimizer, v4.52
10 rows, 9 columns, 21 non-zeros
Preprocessing...
3 rows, 3 columns, 6 non-zeros
Scaling...
 A: min|aij| =  1.000e+00  max|aij| =  1.000e+00  ratio =  1.000e+00
Problem data seem to be well scaled
Constructing initial basis...
Size of triangular part is 3
*     0: obj =   0.000000000e+00  infeas =  0.000e+00 (0)
*     3: obj =   3.500000000e+00  infeas =  0.000e+00 (0)
OPTIMAL LP SOLUTION FOUND
Time used:   0.0 secs
Memory used: 0.1 Mb (126476 bytes)
#OUTPUT:
a[1]: 2
-a[1]: -1
a[3]: 2
#OUTPUT END:
Model has been successfully processed

问题似乎是a[1]被评估为2，而-a[1]被评估为-1。 a [3]也等于2，因此不满足约束p1x3。

目前我不知道如何解决这个问题，甚至是导致问题的原因。

Answer 1

将％d格式说明符更改为％g，看看会发生什么。请注意，{i}是可能具有小数值的连续变量。

GLPK变量似乎在解决后发生变化

1 个答案: