while loop dose not update the variable :(

hello, i am trying to update the value of n in the while loop, but n seem to be equal to 1 all the time, which means that the while loop didn't work.. can you please help the graph should be exponentially decreasing.

b=0;
bits=32;%length of bits in the packet 
E=zeros(1,11);
N=zeros(1,11);
for e=0:0.05:0.5
    packet=round(rand(1,bits));% to make sure the random numbers in the packet contain 1's or 0's in an array 
    ndata =bsc(packet,e);
    totbits=bits;
    cbits=bits;
    n=cbits/totbits; %correct bits over total bits 
    while packet~=ndata
       ndata =bsc(packet,e);
       j=abs(packet-ndata);
       s=sum(j,2);
       c=bits-s;
       cbits=cbits+c;
       totbits=totbits+bits;
       n=cbits/totbits %correct bits over total bits 
    end
    b=b+1
    E(b)= e
    N(b)= n
end 
plot(E,N) 
grid on

[Geoff Hayes]

Noora - what is the bsc function? Is it Model binary symmetric channel? Have you tried stepping through the code (using the MATLAB debugger) to see why the condition on the while loop is never true? Presumably this is the case since you state that your variable (which one?) doesn't update...

[Sudarshan Kolar]

Hello Noora,

I understand that you do not see the values updating in the while loop. I would recommend stepping through your code to better understand what is happening. The following documentations will walk you through code debugging and stepping in Matlab:

https://www.mathworks.com/help/matlab/matlab_prog/debugging-process-and-features.html

Please follow the doc below to observe the values of your variable as you step:

https://www.mathworks.com/help/matlab/matlab_prog/examine-values.html

Hope that helps.

Sudarshan

Answer 1

[James Tursa]

To test if vectors are not equal to each other in an if-test, using the element-wise operator ~= will produce a vector result and then the if-test condition will be a vector. Is this what you intended? Maybe use a different method to compare for inequality here. E.g.,

%    while packet~=ndata
    while ~isequal(packet,ndata)

Although when I make this change, it appears to generate an infinite loop ...