MATLAB: Nested For loop problem

for loopnested loop

Hello all, I am surprised by the thing which is happening to me today. As the following part of code I am using nested for loop.The thing which is troubling me that while running the value of variable Sum_error reaches to the order of 1e27.
Sum_err=0;
last_sum=0;
for k = 1:4;
      clear Sum_err;
      Sum_err=0;
      for n=1:2001
          Env(n)=Peak*exp(-(Ts(n)-Tp)/Tau(k));
          if (Env(n)<=AMt(n))
              Env(n)=AMt(n);
              Peak=AMt(n);
              Tp=Ts(n);
          end
          Sum_err=Sum_err+(Envelope(n)-Env(n))^2;
      end
      MSE(k)=Sum_err/2001;
  end
but when I iterate outer loop just once then the true value(which is expected logically) of Sum_err and MSE come likethis :
Sum_err=0;
last_sum=0;
for k = 5;
      clear Sum_err;
      Sum_err=0;
      for n=1:2001
          Env(n)=Peak*exp(-(Ts(n)-Tp)/Tau(k));
          if (Env(n)<=AMt(n))
              Env(n)=AMt(n);
              Peak=AMt(n);
              Tp=Ts(n);
          end
          Sum_err=Sum_err+(Envelope(n)-Env(n))^2;
      end
      MSE(k)=Sum_err/2001;
  end
Please answer this soon as you figure it out. I will be really grateful to you.
Moreover the full code is here for the sake of completeness.
%Matlab Assignment_1
%Code for simulation of envelope detection
clc;
clear all;
close all;
%AM signal Generation
Ka=.5;
Tm = 5e-4;          
%Time period of message signal
Ts =[0:Tm/1000:2*Tm];       
%Simulation time
Mt = cos(4000*pi*Ts);
%plot(Ts,Mt);
Ct = cos(80000*pi*Ts);
%plot(Ts,Ct);
Envelope=(Ka*Mt+1);
AMt = (Ka*Mt+1).*Ct;
%plot(Ts,AMt);
Tau = [2.5:.5:50]*1e-5;   %96 values
MSE = zeros(1,96);
%Envelope detection
%Tau=1e-4;
Env=zeros(1,2001);
Peak=0.0000;
Tp=0.0000;
Sum_err=0;
last_sum=0;
for k = 1:4;
      clear Sum_err;
      Sum_err=0;
      for n=1:2001
          Env(n)=Peak*exp(-(Ts(n)-Tp)/Tau(k));
          if (Env(n)<=AMt(n))
              Env(n)=AMt(n);
              Peak=AMt(n);
              Tp=Ts(n);
          end
          Sum_err=Sum_err+(Envelope(n)-Env(n))^2;
      end
      MSE(k)=Sum_err/2001;
  end
hold on;
plot(Tau,MSE);
%plot(Ts,Env,'color','red');

Best Answer

You don't need the clear:
clear Sum_err;
Sum_err = 0;
Reinitialize Tp and Peak as well:
for k = 1:...
    Sum_err = 0;
    Tp      = 0;
    Peak    = 0;
    ...
You also don't need to declare them outside of the loop.
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