@tomleslie thankyou Sir. Yes, I forgot to change V back to q[n]....
but how might the constraints be printed one line -one constraint as in the pdf:
This doesn't solve the problem, but it might assist error tracking.
I changed instances of x[cat(i,",",j)] to index(x,i,j) and z[cat(k,",",i)] to index(z,k,i).
"In the above formulation qk = 1 if bin k is chosen. This means that a bin is started with item k in the left bottom position. yi = 1 if item i initializes level i. xij = 1 if item j goes to the level initialized by item i. zki = 1 if item i initializes a level in bin k. "
I suppose the statement in the paper would be difficult to program.
From pp4:" z13 = z27 = z2,10 = 1 means that item 3 initializes level 2 in bin 1 while items 7 and 10 initialize two levels in the second bin which is initialized by item 3. "
About as clear as mud.