can't convert to a number

[Milan Marinkovic]

In my work when I give command solve there is an error:

Error executing "solve" command:

error processing constraint engines['mo','Y1']:

can't convert 'mo' to a number.

Where is:

set J;

set day;

param G{i in day, j in J};

subject to engines {i in day, j in J}: y[i,j] + G[i,j] + (sum{m in J} x[i,m,j]) - (sum{n in J} x[i,j,n]) = y[(i+1),j];

and 

set J := Y1 Y2 Y3 ;

set day := mo tu we th fr sa su;

param G: Y1 Y2 Y3 :=

mo 8 4 4 

tu 7 4 1

we 4 3 4

th 6 3 1

fr 4 4 1

sa 7 5 4

su 10 4 2;

Or see in attachment whole model and data.

[Victor Zverovich]

You using an index over set day in an arithmetic expression i+1, but day contains strings, not numbers. A simple solution is to make set day circular or ordered and use next instead of increment:

  set day circular;

  subject to engines {i in day, j in J}: ... = y[next(i),j];

See section 5.6 Ordered sets of the AMPL book for more details.

HTH,

Victor

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