Syntax Error

[Debbie]

I'm a beginner with AMPL and I can't figure out how to clear up this syntax error at line 22 

param a{0..1};

param b{0..1};

param c{0..1};

param n;

var x {j in 0..n};

var y {j in 0..n};

var z {j in 0..n};

subject to X {j in 0..n} :

sum {j in 0..n} (x[j]) = a[1] - a[0];     ERROR!!!

subject to Y {j in 0..n} :

sum {j in 0..n} (y[j]) = b[1] - b[0];

subject to Z {j in 0..n} :

sum {j in 0..n} (z[j]) = c[1] - c[0]; 

minimize length: (sum {j in 1..n} (sqrt( ((x[j]-x[j-1])/(1/n))^2 +

((y[j]-y[j-1])/(1/n))^2 +

((z[j]-z[j-1])/(1/n))^2) + 10^-6) /n )

subject to speed {j in 1..n} :

sqrt( (x[j] - x[j-1])^2 + (y[j] - y[j-1])^2 + (z[j] - z[j-1])^2  + 10^-6) = sqrt( (x[j+1] - x[j])^2 + (y[j+1] - y[j])^2 + (z[j+1] - z[j])^2  + 10^-6)

data;

param a :=

0 0

1 1 ; 

param b := 

0 0

1 1 ; 

param c := 

0 0

1 1 ; 

param n := 1;

option minos_options "superbasic_limit=500";

solve;

display length;

I'm trying to find the shortest length between 2 points through a finite approximation method of the infinite dimensional problem.

All tips are welcomed!

Thank you!

[Debbie]

The error message that comes out is this:

amplin, line 22 (offset 292):
	syntax error
context:  sum {j  >>> in  <<< 0..n} (x[j]) = abs( a[1] - a[0] );

 Error (2) in /opt/ampl/ampl -R amplin

[victor.z...@gmail.com]

You are trying to redefine dummy index j in a nested indexing expression which is not allowed:

  subject to X {j in 0..n} :

  sum {j in 0..n} ...

To fix it use different names for dummy indices in the constraint indexing and in sum, e.g.

  subject to X {i in 0..n} :

  sum {j in 0..n} ...

HTH,

Victor

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[Indrajit Sen Gupta]

You might have to reformulate your problem since as Victor said you are using the same subscript twice (if you use "i", it needs to be used inside the constraints). Moreover you have missed out semi - colons at couple of places - after the objective function and after the speed constraint.

 

Regards,

Indrajit