我一直在经历 a 的奇怪行为glpsol，更准确地说是它的一个变量。我使用运行命令glpsol -m sol.mod
输入，在文件中sol.mod：
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，甚至不知道是什么原因造成的。