I was wondering if there is a rule or recommendation how to write ordinal expressions if instead of a number, we have a variable or a formula. For example, it is common to come across to the following cases in mathematical and computer science textbooks and papers:
- The ith equation (i=1,2,3,...,n) is solved by...
- Let X(n) denote the best solution found in the nth iteration of the algorithm. We will form a set containing X(n) and all the solutions tested in the nth iteration.
If instead of i and n there were n-1 and i+2, how would we write that in English: n-1st or n-1th, i+2nd or i+2th? How would we deal with more complex expressions such as [n/5]? Is it possible to form such expressions at all or we need to rephrase the sentence?