[Chimera-users] Chimera-users Digest, Vol 38, Issue 12

Jonathan Hilmer jkhilmer at gmail.com
Fri Jun 16 15:15:25 PDT 2006

```Thanks to all for the quick responses on interpolation.

Here's a quick example showing what I was concerned about:

arrows.bld
------------------
.color red
.arrow 0 0 0 1 0 0
.color green
.arrow 0 0 0 0 1 0
.color blue
.arrow 0 0 0 0 0 1
------------------

matrix2
-----------------
Model 0.0
0.505641 0.433743 -0.745785 -2.58211
-0.807506 0.542275 -0.232105 2.90884
0.303746 0.719587 0.624446 -0.194334
-----------------

matrix3
----------------
Model 0.0
0.60158 -0.458982 0.653787 0.653219
0.190507 -0.712397 -0.675423 5.48737
0.775763 0.530872 -0.341124 0.0103466
----------------

The first matrix is just unity.

The 'reset'-based interpolation works great for going between 1 and 3
or 1 and 2 in both directions, as well as 3 to 2, but fails from 2 to
3.  Since all this is new to me, I can't say for certain that this is
due to gimbal lock, but that was my first guess.  I haven't had the
opportunity yet to try out Tom's axis-angle approach, but that should
rule out any Euler problems.  The other problem for me is that all my
current methods are based upon a stepwise approach via commands
(ungainly, but very functional when combined with shell scripts,
imagemagick etc), and this is incompatible with the 'reset'
interpolation.

Perhaps it was misleading to mention the use of 'matrixset'.  I
appreciate that it is more trouble to deal with external files, but if
it is not possible to easily implement the interpolation I'm looking
for dynamically within Chimera's Python (due to required math
libraries, etc) then I would have to hard-code the interpolation
matrices into the .py script file anway, defeating the purpose.

Thanks for the help: I'd love to hear about any future development in this area.

```