Hi guys,

When I try to run the following code:

#Part 0 declaration of parameters

param n;

param m;

set N:=1…n; #number of bonds

set M:=0…m; #number of years

param a{N}; #price of bonds

param L{M}; #liabilities

param d{M,N}; #payment structure

#Part 1 declaration of variables

var x{N} >=0, integer; #investment on bonds

var z{M} >=0; #cash on hand

#Part 2 objective function

minimize cost: sum{j in N} a[j]*x[j];

#Part 3 constraints

subject to initial: z[0]=0;

subject to liability {i in M}: z[i-1]-z[i]+sum{j in N}d[i,j]*x[j]>=L[i];

I ran into the error saying

“Error executing “solve” command:

error processing constraint liability[0]:

invalid subscript z[-1]”

Can anyone help me solving this issue? I’m an absolute rookie to AMPL, any help is appreciated!