如何解码AMPL语法错误？NEOS CPLEX运行MIP报错求助

Hey there, fellow AMPL newbie! Let's break down that confusing syntax error you're seeing—it's a common issue that's easy to fix once you know what's going on.

What's Causing the Error? #

The error message mentions {\rtf1\ansi\ansicpg1252\cocoartf1671—this is a dead giveaway that your model or data file isn't saved as plain text. RTF (Rich Text Format) is a format used by word processors like Microsoft Word, and when you save a file as .txt from those tools, they often sneak in hidden RTF markup that AMPL can't parse. That's why the parser is choking on that weird code at line 9.

Step-by-Step Fixes #

1. Convert Files to Plain Text #

• Open your model and data files in a plain text editor (like Notepad++, VS Code, Sublime Text, or even Windows Notepad/Mac TextEdit—just make sure TextEdit is in "Plain Text" mode first).
• You'll probably see those {\rtf1... lines at the top (or scattered throughout) if the file was saved from a word processor. Delete all that RTF markup.
• Re-save the files: Choose "Save As", set the file type to Plain Text (*.txt), and pick an encoding like UTF-8 or ASCII. Avoid any "Rich Text" or "Word Document" options.

2. Minor Code Tweaks (Optional but Clean) #

While the main issue is file formatting, here are a couple of small adjustments to make your AMPL code more consistent and readable:

• For the Produced variable, instead of combining bounds in one line, separate them into a dedicated constraint (AMPL allows both, but this is easier to debug):

  var Produced{j in 1..m, t in 1..T} integer >= 0;
  subject to ProductionCapacity{j in 1..m, t in 1..T}: Produced[j,t] <= capacity[j];
  

• For the sigma parameter, explicitly define its index to match your model's T parameter (your current code works, but this makes the logic clearer):

  param sigma{t in 1..T} := 1 0.125 2 0.125 3 0.25 4 0.125 5 0.125 6 0.25;
  

Verify Your Fixed Code #

After converting to plain text, your model should look like this (no hidden markup):

# Parameters
param m;
param n;
param T;
param sigma{t in 1..T};
param capacity{j in 1..m};
param demand{i in 1..n};
param cost{i in 1..n, j in 1..m};
param holding;
param InInv{j in 1..m};

# Decision variables
var x{i in 1..n, j in 1..m} binary;
var Produced{j in 1..m, t in 1..T} integer >= 0;
var sold{j in 1..m, t in 1..T} integer >= 0;
var inventory{j in 1..m, t in 0..T} integer >= 0;

# Objective function
minimize TotalCost: sum{i in 1..n, j in 1..m} x[i,j]*cost[i,j] + sum{j in 1..m, t in 1..T}holding * inventory[j,t];

# Constraints
subject to BalanceInventory {j in 1..m, t in 1..T}: Produced[j,t]+inventory[j,t-1]=sold[j,t]+inventory[j,t];
subject to SingleSourcing {i in 1..n}: sum{j in 1..m} x[i,j] = 1;
subject to InitInv {j in 1..m}: inventory[j,0]=InInv[j];
subject to ProductionCapacity{j in 1..m, t in 1..T}: Produced[j,t] <= capacity[j];

Double-check that your data file also has no RTF tags at the top or anywhere else. Once you've done this, upload the plain text files to NEOS CPLEX again, and the syntax error should be gone!

内容的提问来源于stack exchange，提问作者Emil Zacharias Persson