How can I find a connected path on a matrix by Random Search?

Question

bkshn 2014-4-26

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评论： bkshn 2014-5-29

Hello

I have a matrix . I want to find a connected path of elements from up to button. I want to do it by random search. As I said I want connected path ,then if it selects element [i,j] in row i , in the next row (i+1) it should select from column j-1 or j or j+1. I want to do it by random search.

I will appreciate your help.

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Answer 1

rifat 2014-4-27

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编辑：rifat 2014-4-27

在 MATLAB Online 中打开

Hope the following function helps.

function[]= randSelection(mat)
[r c]=size(mat);
list=1:c;
for row=1:r
     col=list(1 + floor(rand() * length(list)));
     l1=col-1;
     l2=col+1;
     if l1<1
         l1=1;
     end
     if l2>c
         l2=c;
     end
     list=l1:l2;
       mat(row,col)
  end

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rifat 2014-5-25

it shows the column index of the elements

bkshn 2014-5-27

编辑：bkshn 2014-5-27

Hello rifat

thanks for your answers.

when I use columnVector(row)=col; within the loop and run the function in debug mode I can see the index of column, But i don't know how can I have it as output of my function in a vector format like [1;2;3;4;4]?

Could you help me?

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Answer 2

Image Analyst 2014-5-27

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Why random? Why not use a function built for it that does it in a systematic way? If you have the Image Processing Toolbox, see http://blogs.mathworks.com/steve/2011/11/01/exploring-shortest-paths-part-1/ Or you could simply use bwlabel() to get a list of all elements on the path.

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Image Analyst 2014-5-27

在 MATLAB Online 中打开

Here I make a matrix that has a roughly "S" shaped path. Then I run rifat's code on it:

function test
clc;
mat = [...
  0 0 0 1 1 1 0
  0 0 1 0 0 0 0
  0 1 0 0 0 0 0
  0 0 1 1 1 0 0
  1 0 0 0 1 0 0
  0 1 1 0 0 1 0
  0 0 0 1 1 1 0
  0 0 0 0 0 0 0]
  
randSelection(mat)
function[]= randSelection(mat)
[r c]=size(mat);
list=1:c;
for row=1:r
  col=list(1 + floor(rand() * length(list)));
  l1=col-1;
  l2=col+1;
  if l1<1
    l1=1;
  end
  if l2>c
    l2=c;
  end
  list=l1:l2;  
  mat(row,col)
end

Save all of the above code (both functions) in test.m and run it and you'll get this:

mat =
     0     0     0     1     1     1     0
     0     0     1     0     0     0     0
     0     1     0     0     0     0     0
     0     0     1     1     1     0     0
     1     0     0     0     1     0     0
     0     1     1     0     0     1     0
     0     0     0     1     1     1     0
     0     0     0     0     0     0     0
ans =
     0
ans =
     0
ans =
     0
ans =
     1
ans =
     1
ans =
     0
ans =
     1
ans =
     0

Now if that's what you want, fine, but I'm just not getting it. I don't see anything that describes the location of the pixels (elements) on the "S" shaped path. I would think the path would be a list of 16 (row, column) coordinates, not a list of 8 zeros or ones (not even really a list since they're not in the same array). But I'm glad it's working for you. I don't need to understand it - you do and that's all that counts.

bkshn 2014-5-29

Yes You are right. as you see in rifat's code , it selects one random element in each row. but I want to have them as a vector with number of columns. for example I want [3;4;2;1;....] to show me index of columns each random element, I want rifat to explain me more and help me how can I have a vector as output.

Could you help me?

I want to do random search on a matrix to find shortest path.

I'll appreciate your help.

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