Absolute value of coordinate trace.
u=abs(t)
Taking the absolute value of a coordinate trace changes all coordinates with negative directions to their positive counterparts.
>> t=imat_ctrace('101x-', '55z', '75y-')
t =
'101X-'
'55Z+'
'75Y-'
>> abs(t)
ans =
'101X+'
'55Z+'
'75Y+'