Select certain sub-matrix from matrix

Hi everyone, I have a matrix in such form that:

   1 1 1 1 1 1 1 1 1 1 
   0 1 1 1 1 1 1 1 1 1 
   1 0 1 1 1 1 1 1 1 0 
   1 1 0 1 1 1 1 0 0 1 
   1 1 0 0 0 0 0 1 1 1

I would like to single out the sub-matrix enclosed (above zeros) by zero elements, and set them all to zero as well. I knew it can be done by a simple for loop, since I need to run it many times, I want to vectorize the process. Thanks in advanced for any help and suggestion.

[Vaclav Rimal]

Playing go?

[Thomas]

No. I am dealing with surface evolution, but it looks just like Go :)

[KSSV]

Question is not clear......can you tell me the sub matrix you are expecting from the given matrix? Better type the matrix.

[Vaclav Rimal]

After your edit, the problem became more simple. What about this (suppose your original matrix is called a):

[m,pos]=min(a);
for i=1:size(a,2)
  a(1:pos(i),i)=0;
end

However, I can't think of any way to avoid the for cycle. Probably indexing the matrix elements in the column-vector, one-index manner?

Answer 1

[Guillaume]

If all you want to do is propagate the zeros upward then a cumprod on the flipped up-down matrix is all that's needed:

a = [1 1 1 1 1 1 1 1 1 1
     0 1 1 1 1 1 1 1 1 1
     1 0 1 1 1 1 1 1 1 0
     1 1 0 1 1 1 1 0 0 1
     1 1 0 0 0 0 0 1 1 1];

flipud(cumprod(flipud(a)))