Description

This demonstrates the problems with a stateful function library in
the context of GAMS and solver processes.

The trilib default mode for computations is in radians (mode=0). The
function SetTriMode can be used to interpret the arguments of
subsequent function calls to Cosine and Sine as degrees (mode=1)
instead of radians (mode=0). The SetTriMod function returns the
previous mode value.

Contributor: Michael Bussieck

Small Model of Type : GAMS

Category : GAMS Test library

Main file : trilib04.gms   includes :   compilec.inc [html]  precomp.inc [html]

$Title Demonstrates problems with a stateful function library (TRILIB04,SEQ=552)

$ontext
This demonstrates the problems with a stateful function library in
the context of GAMS and solver processes.

The trilib default mode for computations is in radians (mode=0). The
function SetTriMode can be used to interpret the arguments of
subsequent function calls to Cosine and Sine as degrees (mode=1)
instead of radians (mode=0). The SetTriMod function returns the
previous mode value.

Contributor: Michael Bussieck
$offtext


$ifThen set nocomp
*  Use precompiled library provided by testlib
$  batinclude precomp.inc tricclib
$else
*  Compile library from source code
$  batinclude compilec.inc tri
$endIf

function mySetTriMode / myLib.SetTriMode /
         myCos        / myLib.Cosine     /;

variable x, y; equation e;
e..   x =e= mycos(y);
model m /e/;

* Everything is default, so in radians
y.fx = pi/2;
solve m min x using nlp;
abort$(abs(x.l-0)>1e-12) 'x<>0';

display$mySetTriMode(1) 'Now we switch to degrees but do solvelink=ChainScript';

* The solver runs in a separate process and we start with a new function library instance with default state (i.e. mode=0)
m.solvelink=%solvelink.ChainScript%;
solve m min x using nlp;
abort$(abs(x.l-0)>1e-6) 'x.l expected to be 0', x.l;

* Since GAMS solve restarts with a new process and a default state library mode was 0
abort$(0<>mySetTriMode(1)) 'mode expected to be 0';

* Now the same with solvelink=CallModule, where we have a solver process, but GAMS stays memory resident
m.solvelink=%solvelink.CallModule%;
solve m min x using nlp;
abort$(abs(x.l-0)>1e-6) 'x.l expected to be 0', x.l;
abort$(1<>mySetTriMode(1)) 'mode expected to be 1';

* Now the same with solvelink=LoadLibrary, where we have a solver library linked into GAMS
m.solvelink=%solvelink.LoadLibrary%;
y.fx=90;
solve m min x using nlp;
abort$(abs(x.l-0)>1e-6) 'x.l expected to be 0', x.l;
abort$(1<>mySetTriMode(1)) 'mode expected to be 1';