I coded a script in php that generates the new Model A tables. Heres a short snipet of the code that tells you if the type model starts with a + or -.

$arg1, is the second letter of the type i.e. For the ENTp it would be N
$arg2, is the third letter of the type i.e. For the ENTp it would be T

Essentially if the transittion is as follows
-> N -> F -> S -> T -> N
Then its a minus.

Essentially if the transittion is as follows
<- N <- F <- S <- T <- N
Then its a plus.


function isplus($arg1,$arg2)
{
if ($arg1 == 'N' && $arg2 == 'F')
{$ret = false;}
if ($arg1 == 'F' && $arg2 == 'S')
{$ret = false;}
if ($arg1 == 'S' && $arg2 == 'T')
{$ret = false;}
if ($arg1 == 'T' && $arg2 == 'N')
{$ret = false;}
if ($arg1 == 'N' && $arg2 == 'T')
{$ret = true;}
if ($arg1 == 'T' && $arg2 == 'S')
{$ret = true;}
if ($arg1 == 'S' && $arg2 == 'F')
{$ret = true;}
if ($arg1 == 'F' && $arg2 == 'N')
{$ret = true;}
return $ret;
}

Took me a while to figure it out. At first it seems like theres a clear pattern, then after examination it gives you a head ache, then Aha! The pattern is found. Hope this helps.