如何从文件中读取单个参数？

Question

AMPL book 的第 9 章第 163 页给出了从文件中读取单个参数的示例：

For example, if you want to read the number of weeks and the hours available each week for our simple production model (Figure 4-4),

param T > 0;

param avail {1..T} >= 0;

from a file week_data.txt containing

4

40 40 32 40

then you can give the command

read T, avail[1], avail[2], avail[3], avail[4] <week_data.txt;

此命令在 GLPK 中失败，错误为 colon missing where expected。建模语言 GNU MathProg 语言参考仅包含 table data IN，用于读取表格数据。 GLPK 可以从文件中读取单个参数吗？

Answer 1

您可以使用 table 语句从 CSV 文件或 SQL tables 中读取参数。

您可以使用数据文件来传递参数，例如参见 this example of writing data files in AWK and Visual Basic。

Answer 2

AMPL 和 GMPL 是相关的函数式语言。 GMPL 包含 AMPL 语法的一个子集，但在几个方面有所不同，例如 table 语句。

读取单个参数的一种方法是使用特定语法将数据写入文件，例如下面的内容显示了一个参数和一个 table:

param T := 4;

param avail :=
      1 0
      2 1
      3 1
      4 0;

end;

要验证语法，请考虑文件 problem.mod:

中的这段代码

param T > 0;

param avail {1..T} >= 0;

var use {1..T} >= 0;

maximize usage: sum {t in 1..T} avail[t];

subject to constraint {t in 1..T}: use[t] <= avail[t];

solve;

end;

结果表明成功了：

> glpsol -m problem.mod -d problem.dat
GLPSOL: GLPK LP/MIP Solver, v4.65
Parameter(s) specified in the command line:
 -m problem.mod -d problem.dat
Reading model section from problem.mod...
13 lines were read
Reading data section from problem.dat...
9 lines were read
Generating usage...
Generating constraint...
Model has been successfully generated
glp_mpl_build_prob: row usage; constant term 2 ignored
GLPK Simplex Optimizer, v4.65
5 rows, 4 columns, 4 non-zeros
Preprocessing...
~     0: obj =   2.000000000e+00  infeas =  0.000e+00
OPTIMAL SOLUTION FOUND BY LP PREPROCESSOR
Time used:   0.0 secs
Memory used: 0.1 Mb (110236 bytes)
Model has been successfully processed

如何从文件中读取单个参数？

How to read single parameter from a file?

glpk