We have found a bug in previously released versions of the VA-TWIST program that in some cases will produce an incorrect value for the angle of the principal axes. An incorrect value will be reported whenever the first principal direction is negative, i.e., between 0 and -90 degrees from the x axis. If the first principal angle is positive, the reported value is correct. To fix the bug please make the following change in the Subroutine secprop at approximately line 1428 of the program and recompile the program:

if(sec_hxy/sec_j.lt.1.d-14)then

if(dabs(sec_hxy/sec_j).lt.1.d-14)then

Note that this bug does not affect any other solution values except for the reported angle of the principal axes.

We would be very grateful if you would pass along this information to anyone you know who has a copy of the VA-TWIST program.

Thank you,

Gary S. Beaupré, PhD