Rotation matrix

[Philippe Hurbain]

I am trying to calculate what a', b', c', etc. (with apostrophe) of a MPD sub-model would be after processing the model. The values of a, b, c, etc. (without apostrophe) are obviously already known.

Sorry, misunderstood... You then need to perform a matrix multiplication.
if you have a submodel sm.dat containing reference to xxx.dat as

Code:

1 16 x y z a b c d e f g h i xxx.dat

and a model m.dat using transformed submodel sm:

Code:

1 16 x' y' z' a' b' c' d' e' f' g' h' i' sm.dat

then model m can be expressed as a transformed xxx.dat as

Code:

1 16 x" y" z" a" b" c" d" e" f" g" h" i" xxx.dat

with

Code:

x"=a'x+b'y+c'z+x'
y"=d'x+e'y+f'z+y'
z"=g'x+h'y+i'z+z'

and

Code:

a"=a'a+b'd+c'g
b"=a'b+b'e+c'h
c"=a'c+b'f+c'i
d"=d'a+e'd+f'g
e"=d'b+e'e+f'h
f"=d'c+e'f+f'i
h"=g'a+h'd+i'g
h"=g'b+h'e+i'h
i"=g'c+h'f+i'i

You can find gazillion of stuff on the web about matrix multiplication... hopefully you can wrap your head about it!
One big thing to remember, order of matrix IS significant. matrix A * matrix B is different from matrix B * matrix A!!!