Re: ...Contemplating unspecified constraint SOLVERS.

On Sat, 27 Aug 2005 10:44:57 -0400, "Dirk Mittler"
<mdirk@xxxxxxxxxxxx> wrote:

>It was never my intention to complain. {:-)} And I thank you for pointing
>out that in constraint solvers, "labelling" is an important step. I will
>look up the subject in more detail then, when I find the time. For now I
>*imagine* that labelling could satisfy this need of assigning to the
>attributed variables, after constraints have been specified. This could be
>why in one Prolog example which I've seen, the 'label' command is given last
>over several variables to tell the compiler to solve. It will intrigue me
>then to learn how this command really works.

"labeling" in its simplest form is pretty dumb procedure that uses
trial-and-error method to "assign" values to domain variables
("asign" means selecting a value from variable's domain). It works
more or less this way:

1. Select values from domains of all variables and check
constraints,
2. If constraints satisfied, you have solution. If all values have
been tested, there is no solution
3. If not, change value of one selected domain variable and go to 2

Clearly, there are some technical details how to arrange this
process and make it efficient. See Apt book on constraints about
details of this process.

Advise:

Get ECLIPSE Prolog. Although registration is required, it is free
for non comemrcial applications. It comes with EXTREMELY good
tutorial on Prolog and constraint programming. In chapter 12 you
will find a lot information about constraints, labeling and problem
solving.

Tutorial is here

http://www.icparc.ic.ac.uk/eclipse/reports/tutorial58.pdf

To get ECLIPSE go here

http://www.icparc.ic.ac.uk/eclipse/

A.L.
.

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