Hi,
I am trying to solve the Lennard-Jones cluster problem with 5 atoms on the NEOS solver. Here is the GAMS model:
Scalar e /0/;
Positive variables x2,x3,y3,x4,y4,z4;
Variables x5,y5,z5;
Variable obj;
x2.up=1.2;
x3.up=1.2;
y3.up=1.2;
x4.up=1.2;
y4.up=1.2;
z4.up=1.2;
x5.lo=-1.2;
x5.up=1.2;
y5.lo=-1.2;
y5.up=1.2;
z5.lo=-1.2;
z5.up=1.2;
equations objdef;
objdef… obj =e=
(4sqr(1/(x2**6+e)-1/2)-1)+(4sqr(1/((sqr(x3)+sqr(y3)+e)**3)-1/2)-1)+(4sqr(1/((sqr(x4)+sqr(y4)+sqr(z4)+e)**3)-1/2)-1)+(4sqr(1/((sqr(x5)+sqr(y5)+sqr(z5)+e)**3)-1/2)-1)
+(4sqr(1/((sqr(x3-x2)+sqr(y3)+e)**3)-1/2)-1)+(4sqr(1/((sqr(x4-x2)+sqr(y4)+sqr(z4)+e)**3)-1/2)-1)+(4sqr(1/((sqr(x5-x2)+sqr(y5)+sqr(z5)+e)**3)-1/2)-1)
+(4sqr(1/((sqr(x4-x3)+sqr(y4-y3)+sqr(z4)+e)**3)-1/2)-1)+(4sqr(1/((sqr(x5-x3)+sqr(y5-y3)+sqr(z5)+e)**3)-1/2)-1)
+(4sqr(1/((sqr(x5-x4)+sqr(y5-y4)+sqr(z5-z4)+e)**3)-1/2)-1)
Model m / all /;
Solve m minimizing obj using nlp;
Display obj.l;
and options
optca 1e-3
optcr 0
MaxTime 60
BARON immediately fails with this message:
**** Exec Error at line 32: division by zero (0)
However, when the variable e is given a small value (e.g. 1e-9), BARON reaches convergence.
I have tried giving the variables an initial value, without success.
Could you help me out?
Thanks,
Charlie
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