passiveForceLengthCurve.m

% This function is part of the NMSM Pipeline, see file for full license.
%
% This function calculates the normalized passive force
%
% (Array of number) -> (Array of number)
% returns normalized passive force  


function normalizedPassiveForce = passiveForceLengthCurve(...
    normalizedMuscleFiberLength)

e1 = 0.232000797810576;
e2 = 12.438535493526128;
e3 = 1.329470475731338;
% Result of exp can be greater than a double can store
% normalizedPassiveForce = e1 * log(exp(e2 * (... 
%     normalizedMuscleFiberLength - e3)) + 1);

fiberLengthPower = e2 * (normalizedMuscleFiberLength - e3);
normalizedPassiveForce = e1 * (log(exp(0.5 * fiberLengthPower) + ...
    exp(-0.5 * fiberLengthPower)) + log(exp(0.5 * fiberLengthPower)));
end