Problem with "if ~isempty" and "break" in a while loop

Hello I'm running the following code but it seems that in the lines

if ~isempty(cols_withonly0) 
col_0=cols_withonly0(1);
   else
       break
end

the condition ~isempty(cols_withonly0) is not recognized and the "break" in the while loop occurs before filling the pixl_list matrix with non zero values. "fi" and "IM" are 2000*2992 matrix with non zero values. When I run the code without the lines "if ~isempty(cols_withonly0)", "else", "break", "end" the "pixl_list" is filled as I want but I have an error message at the end because "cols_withonly0" is empty and cols_withonly0(1) exceeds array bounds. Do you have an idea where the mistake is and how to fix it to fill the "pixl_list" properly?

Thank you in advance for your answers!

pi_min=round(-pi,1);
pi_max=round(pi,1);
Non0_IM = length(find(nonzeros(IM)));
   Non0_pxllist= 0;
   N_max=Nx*Ny;

   while Non0_IM > Non0_pxllist && pi_min < pi_max
     for k=pi_min:0.1:pi_max
       pos=(k+round(pi,1))*10+1; 
       pos=round(pos);
       posi(pos)=pos;
       ka(pos)=k;
       [fila columna]=find(fi==k);
           for ind=1: length(fila)
       fifi=fila(ind);
       coco=columna(ind);
       pixl=IM(fifi, coco);
       pixl_list (pos,ind)= pixl;
           end
     end 
     
   Non0_pxllist= length(find(nonzeros(pixl_list)));
   cols_withonly0=find(all(pixl_list==0));
  
   if ~isempty(cols_withonly0)
   col_0=cols_withonly0(1);
   else
       break
   end
   pi_min=ka(col_0);
   pi_max=pi_min;  
   end

[Jan]

I've formatted the code to improve the readability.

Please post some test data, e.g. created by rand(). Otherwise we cannot run your code to see, what happens.

Notes:

nnz(IM)   % nicer and faster than: length(find(nonzeros(IM)))

The expression "all(pixl_list==0)" is dangerous, if it is not clear if the argument is a matrix or a vector. It is safer to specify the dimension to operate on: all(pixl_list==0, 1)

[Martina Clairand]

Hello,

thank you for your quick answer. I can't provide the original matrix because I extracted them from an image. But matrix with random values work for running the code. For example we can use fi= randi([1 10], 2000,2992) and IM= randi([-500 500], 2000,2992). The most important thing is to be able to fill "pixel_list " with the 5984000 values contained in "IM" (2000*2992= 5984000 ).

Thank you for your help!

[Martina Clairand]

Sorry I noticed I made a mistake: "fi" should contain values between -pi and pi so its better if we assume fi= round(randi([-3, 3], 2000,2992)/2+1.2, 1) to run the code.

Bests

[Steven Lord]

Please set a breakpoint on the line containing that break statement and show us the output of the following command executed when MATLAB stops at that breakpoint:

   whos cols_withonly0 pixl_list

[Martina Clairand]

Hello, I obtained this:

Name Size Bytes Class Attributes

cols_withonly0 1x0 0 double

pixl_list 63x232552 14650776 uint8

[dpb]

Certainly doesn't seem to be an issue there; it would be beneficial to see a run and the complete error message in context as well.

Just from a stylistic point, the code would be easier to read if it were written as

if isempty(cols_withonly0)
  break
else
  col_0=cols_withonly0(1);
end

Although as posted the irregularity in the indenting makes the code hard to read; it would seem the above could also be simplified to just

...
if isempty(cols_withonly0), break; end
col_0=cols_withonly0(1);
...

since the remainder of the loop isn't executed anyway.

[Martina Clairand]

ok thank you!