Re: [Help-glpk] Error : multiplication of linear forms not allowed

[Andrew Makhorin]

> In my previous post I have been wrong in identifying the constraint.
> What I actually need is something like XOR operator, not AND operator,
> i.e. z[i] = p[i] xor p[i+1]

> I tried to write this as follows, s.t. cntr1{i in PROCESSES}: z[i] =
> ((p[i] + (if i < 6 then p[i+1] else 1)) mod (2));

> This gives me an error "operand preceding mod has invalid type",
> please help me to get this corrected.

Let x and y be binary variables. Imagine that you add them that gives
a two-bit sum cs. Then:

   x + y = 2 * c + s,

where c = (x AND y) is the carry bit, and s = (x XOR y) is the sum bit.