MATLAB: Unable to perform assignment because the left and right sides have a different number of elements.

matlab error

I wrote this code, but I'm always getting "unable to perform assignment because the left and right sides have a different number of elements." 
clearvars; close all; clc;
% rate
rI = 2; 
rp = rI/100;
dp = rp;
KP = 40000;
beta = 2000;
tmax = 500; 
time = 0:.1:tmax;
% pre-allocate for I
I = zeros(length(time), 1);
% initial I
I(1) = 50;
% pre-allocate for P
P = zeros(length(time), 1);
% initial P
P(1) = 1100;
for t = 1:length(time)-1
    I(t+1) = I(t) + ( (rI * I(t)) * (1 - (I(t) / f(P)))) - ((beta * (I(t).^2)) / ((g(P).^2) + (I(t).^2)));
    P(t+1) = P(t) + (rp * P(t)) * (1 - (P(t) / KP)) - (dp * I(t));
end
%%%%%%%%% functions %%%%%%%%
function KI = f(P)
KI = 4*P;
end
function alpha = g(P)
alpha = P/2;
end

Best Answer

for t = 1:length(time)-1
  I(t+1) = I(t) + ( (rI * I(t)) * (1 - (I(t) / f(P(t))))) - ((beta * (I(t).^2)) / ((g(P(t)).^2) + (I(t).^2)));
  P(t+1) = P(t) + (rp * P(t)) * (1 - (P(t) / KP)) - (dp * I(t));
end
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