Need help

close all
clear
clc

%TESTING OF PLL
Ac=1;   fc=10;  fs=1000;    Ts=1/fs;

initial_phase=65;   learning_coefficent=10;  t=0:Ts:1;

pure_carrier=Ac*sin(2*pi*fc*t+initial_phase); %its vector samples:Ac*exp(1i*initial_phase)

Speed_of_light=300000000;   Distance=300;   Speed=36.1; % in meters per second

Theoretical_Dopp_Freq=-fc/Speed_of_light*Speed^2*t./sqrt(Speed^2*t.^2+Distance^2);
Theoretical_Phase=initial_phase-(2*pi*fc*sqrt(Speed^2*t.^2+Distance^2))./Speed_of_light;

Phase_estimate=zeros(1,length(pure_carrier));   error_signal = zeros(1, length(pure_carrier));

%Initial Estimation
error_signal(1)=imag(pure_carrier(1)*exp(-1i*Phase_estimate(1)));

for n=2:length(pure_carrier)
    error_signal(n)=imag(pure_carrier(n)*exp(-1i*Phase_estimate(n)));
    Phase_estimate(n) = Phase_estimate(n-1) + learning_coefficent*(imag(pure_carrier(n-1)*exp(-1i*Phase_estimate(n-1))));
end

% Generate the PLL output signal
figure(1)
plot(error_signal),title('Vector of Error Signals');