From: sunyeping (sunyeping_at_aliyun.com)
Date: Thu Sep 29 2016 - 04:49:57 CDT

Dear all,
I've selected two groups of atoms ($sel1 and $sel2) and by using the orient package I can calculate the principal axes of these two selections:
set I1 [Orient::calc_principalaxes $sel1] 
set I2 [Orient::calc_principalaxes $sel2]
Now I want to calculate the angle between the first principal axis of $sel1 and the second axis of $sel2. What is the correct command for doing this? I guess it is not:
    set angle [Orient::orient $sel1 [lindex $I1 0] [lindex $I2 1]]
because it gives the  following output:
    Total weight: 94026.05758213997
    {0.6035130023956299 -0.7008411884307861 0.3802546560764313 -19.113555908203125} {0.3327126204967499 0.6547419428825378 0.6786864399909973 -3.631439208984375} {-0.7246201634407043 -0.2830805778503418 0.6283239722251892 -13.903969764709473} {0.0 0.0 0.0 1.0}
I don't understand what it means but it seems to have nothing to do with angle. 
Could you help me with this?
Best regards.
Yeping Sun