parrm.m

书籍“Regularization tools for training large feed-forward neural networks using Automatic Differentiat

function[alpha] = parrmV1(v0, v1, v2, alpha_in)

v1n = norm(v1)^2;
v2n = norm(v2)^2;

a1 = (1.5*v1'*v2)/v2n;
a2 = (v0'*v2+.5*v1n)/v2n;
a3 = (0.5*v0'*v1)/v2n;

aa(1) = 1;
aa(2) = a1;
aa(3) = a2;
aa(4) = a3;

rr = roots(aa);
rr = rr(find(imag(rr)== 0));
rr = rr(find((rr) > 0));

if length(rr) == 0,
   alpha_p = alpha_in; 
else
   alpha_p = min(rr);
end

if alpha_p >= alpha_in 
    alpha = alpha_in/2;
else
    alpha = max(alpha_in/8, alpha_p);
end