not entering nested for loop

So I am averaging the values of a few pixels in a an area specified by the two for loops parameters (l&m). However, I must be staring at this code for too long as it is not entering the nested loop resulting in an average of zero... which it shouldn't be.

The pixel values of 0 & 12 correlate to black and white which is why they are over-written to not be included in the image due to some of the image having text and lines on top of it...

tic
localurl='http://www.ips.gov.au/Images/HF%20Systems/Global%20HF/Ionospheric%20Map/WorldIMap0.gif';
% [stat, h, localurl]=web(localurl);%doesnt have to run this line
[mat,map]=imread(localurl);
colormap(map);%doesnt have to run this line
image(mat);%doesnt have to run this line

c=clock;
year=num2str(c(1));
month=num2str(c(2));
day=num2str(c(3));
hour=num2str(c(4));
min=num2str(c(5));

savename=[year '.' month '.' day '.' hour '.' min '.fig'];

savefig(savename)
.
.
.
s=1;
value=zeros(1,1);
for l=178:184
    disp('1st')
    for i=224:218

          disp('2nd')
          value(s)=mat(m,l);
          if value(s)~=0 && value(s)~=12
              s=s+1;
          end
      end
  end
  avg=mean(value(:));

toc

Answer 1

[Jan]

• Your inner loop does not depend on "i", but there is an orphaned "m" without a definition.
• The inner loop goes fro 224 to 218, but the first index is larger than the second one.

I guess your loop code can be simplified:

data = mat(218:224, 178:184);
avg  = mean(data(data ~= 0 & data ~= 12))

[Adrienne]

thank you so much, and ya i is m I had been messing with some values and forgot to change it back!

Answer 2

[dpb]

s=1;
value=0;
for l=178:184
  for i=224:218
    value(s)=mat(m,l);
    if value(s)~=0 && value(s)~=12
      s=s+1;
    end
  end
end
avg=mean(value(:));

value(s)=mat(m,l);

What's m??? It's never update in the loop so you're always looking at the same pixel. Or, looking again I suppose you meant to write

     for m=224:218

instead of i for the inner loop.

The above could be simply

    c1=178; c2=184;
    r1=224; r2=218;
    avg=mean(mat(mat(r1:r2,c1:c2)~=0 & mat(r1:r2,c1:c2)~=12));