One nonzero in set of free variables

In [1] the following question is posed:

I have free variables \(\color{darkred}x_i\). How can I impose the constraint that at least one of the variables is nonzero: \(\color{darkred}x_i\ne 0\).

Informs Test of Time Award for CONOPT paper

The Test of Time Award for papers published in the INFORMS Journal on Computing in the years 1993–1997 is awarded to

CONOPT: A Large-Scale GRG Code

Arne Stolbjerg Drud

ORSA Journal on Computing 6(2):207–216, 1994 

As Arne notes in [1], he is helped a bit by the fact that CONOPT users may want to cite a published paper (and because there is no newer successor paper). Still, this is quite an achievement. 

GAMS listing file: missing Unicode support

Newer versions of GAMS allow UTF-8 encoded strings as labels. That is very welcome, as these labels may come from data sources that just use Unicode characters. However, when printing to the listing file, we miss proper Unicode support. At first, I thought, "OK, just a few misaligned tables. No big deal." Here is a constructed example showing this may be a bit more problematic.

String Art

 

In [1], a greyscale picture is approximated by strings (lines) between points around the image. Here, I will try something similar with a formal optimization model.