Looks to be in the calling/use of F2, the functions themselves appear to be OK.
Although from a sytlistic standpoint you could save a little code in F1 by writing
r=ones(size(t)); % preallocate; set to 1
mask= (t<=27); % set the range to use correlation results
r(mask) = p1*t(mask).^4 + p2*t(mask).^3 + p3*t(mask).^2 + p4*t(mask) + p5;
that saves one logical operation by setting all to 1 first, then fixing up those not to be 1. (I also introduced a set of parentheses that make, for me, the logical vector definition easier to read although they're not needed for syntax.)
One other shorthand using MATLAB builtin functions would be
function r = F1(t)
r=ones(size(t)); % preallocate; set to 1
p = [2.585e-6, -9.23e-5, 0.001032, -0.002989, 0.7562]; % put poly coeff in array
mask= (t<=27); % set the range to use correlation results
r(mask) = polyval(p,t(mask)); % let polyval() do the hard work to evaluate
end
