lookup(): "i" option?

[Olaf Till]

Hi,

a problem occured in optimset.m, optimget.m, __all_opts__.m, which
seemed due to the usage of lookup(..., ..., "i"). A description of the
problem and a suggested fix are already on the bug-tracker, but I
thought the issue with lookup(..., ..., "i") should also be discussed
here.

I would suggest that the "i" option of lookup() should be dropped,
since lookup() requires a sorted table, while case-insensitivity makes
the sorting-criteria undefined.

An illustration of the problem:


## tbl is sorted with respect for normal lookup
octave:1> tbl = {"Ab", "aa", "c"};
octave:2> lookup (tbl, "aa")
ans =  2
## for case-insensitive lookup, tbl is not correctly sorted
octave:3> lookup (tbl, "aa", "i")
ans = 0
octave:4> 

lookup(,, "i") internally converts to uppercase, so one could supply a
table correctly sorted in uppercase; but this solution is only valid
as long as lookup() indeed internally converts to
uppercase. Essentially, the correct sort order is just undefined when
case-insensitivity is used.

Olaf