Index through 2 vectors to determine if 1 contains a subset of the other, return the index of each vector where they synchronize

I have 2 large vectors of differing sizes, technically, one vector should contain a subset of the other, but I need to prove that out. Prior to synchronizing, each vector will have non-matching length of buffer data before they line up. A small example would look like:

set1 = [9 7 9 5 1 2 3 4 5];

set2 = [8 6 1 2 3 4 5];

I would like to return the index of each vector that points to where synchronization begins.

Answer 1

[Liam]

Assuming the buffer is only at the start of each vector, something like this should work.

[a,b] = synchindex(set1,set2)

function [a,b] = synchindex(set1,set2)
  a = length(set1);
  b = length(set2);

  if set1(a) ~= set2(b)
    a = ('no match');
    b = ('no match');
  else if set1(a) == set2(b)
      while set1(a-1) == set2(b-1)
          a = a - 1;
          b = b - 1;
      end
  else
    a = ('no match');
    b = ('no match');
  end
end
end

[Voss]

set1 = [9 7 9 5 1 2 3 4 5];
set2 = [8 6 1 2 3 4 5];
[a,b] = synchindex_modified(set1,set2)

a = 5

b = 3

[a,b] = synchindex_original(set1,set2)

a = 5

b = 3

set1 = [9 7 9 5 1 2 3 4 5];
set2 = [8 6 1 2 3 4 6];
[a,b] = synchindex_modified(set1,set2)

a = NaN

b = NaN

[a,b] = synchindex_original(set1,set2)

a = 'no match'

b = 'no match'

set1 = [1 2 3 4 5];
set2 = [1 2 3 4 5];
[a,b] = synchindex_modified(set1,set2)

a = 1

b = 1

[a,b] = synchindex_original(set1,set2)

Array indices must be positive integers or logical values.

Error in solution>synchindex_original (line 24)
while set1(a-1) == set2(b-1)

function [a,b] = synchindex_original(set1,set2)
  a = length(set1);
  b = length(set2);
  
  if set1(a) ~= set2(b)
    a = ('no match');
    b = ('no match');
  else
    if set1(a) == set2(b)
      while set1(a-1) == set2(b-1)
        a = a - 1;
        b = b - 1;
      end
    else
      a = ('no match');
      b = ('no match');
    end
  end
end


function [a,b] = synchindex_modified(set1,set2)
    a = numel(set1);
    b = numel(set2);
    if set1(a) ~= set2(b)
        a = NaN;
        b = NaN;
        return
    end
    while a > 1 && b > 1 && set1(a-1) == set2(b-1)
        a = a - 1;
        b = b - 1;
    end
end

[Liam]

Nice improvement, thanks!