/usr/share/psychtoolbox-3/Psychometric/FindAlphaWeibTAFC.m is in psychtoolbox-3-common 3.0.11.20140816.dfsg1-1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | function alpha = FindAlphaWeibTAFC(pCorrect,threshold,beta)
% threshold = FindThreshWeibTAFC(pCorrect,threshold,beta)
%
% Find alpha so that the Weibull function with passed beta
% predicts the pCorrect threshold to be the passed value
% of threshold.
%
% This computation is mostly useful for testing.
%
% 8/25/94 dhb, ccc Wrote it.
if (pCorrect <= 0.0 || pCorrect > 1.0)
error('pCorrect is out of bounds');
end
% Find the alpha. We didn't really think about this, we just
% assumed that the code in FindThreshWeibTAFC was correct and
% went from there.
alpha = threshold ./ ( -1.0*log(2.0 .* (1.0-pCorrect))) .^(1.0./beta);
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