/usr/share/psychtoolbox-3/PsychGamma/InitialXPow.m is in psychtoolbox-3-common 3.0.11.20131230.dfsg1-1build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | function x = InitialXPow
% x = InitialXPow
%
% Initial values for power function fit.
x = [0.01]';
|