Mathematical Functions in Nuke Cheat Sheet

Adding Mathematical Functions to Expressions in Nuke

atop = AB+B(1-A)
average = (A+B)/2)
color-burn = Darken B towards A
color-dodge = brighten B towards A
conjoint-over = A+B(1-a/b), A if a>b
copy = A
difference = abs(A-B)
disjoint-over = A+B(1-a)/b, A+B if a+b<1
divide = A/B, 0 if A<0 and B<0
exclusion = A+B-2AB
from = B-A
geometric = 2AB/(A+B)
hard-light = multiply if A<0.5, screen if A>0.5
hypot = sqrt (A*A+B*B)
in = Ab
mask = Ba
matte = Aa+B(1-a)
max = max (A,B)
min = min (A,B)
minus = A-B
multiply = AB, A if A<0 and B<0
out = A(1-b)
over = A+B(1-a)
overlay = multiply if B<0.5, screen if B>0.5
plus = A+B
screen = A or B ≤1? A+B-AB: max(A,B)
soft-light = Image B gets lit up.
stencil = B(1-a)
under = A(1-b)+B
xor = A(1-b)+B(1-a)

http://help.thefoundry.co.uk/nuke/content/comp_environment/expressions/adding_math_functions.html