MATLAB: Sum values in a vector to extract nth term into new matrix

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Hello,
I have a matrix:
A =
      3.0000    2.2200
      5.0000    2.2187
      7.0000    2.2171
      9.0000    2.2132
     11.0000    2.2168
     13.0000    2.2277
     15.0000    2.2283
     19.0000    2.2451
I want to take first value and put in new matrix:
[ExtractedA] = A(1,:);
Then, I want it to find the next value that is >= 20; i.e. First values in ExtractedA are:
3.0000    2.2200
9.0000    2.2132          %this value because +5+7+9 = 21 (which is >=20)
Then, I need it to start again looking for the next +20 after the 9:
13.0000    2.2277          %this would be next, since 11+13 >= 20.
Any help on the best function to do this? I know this is likely trivial, but my searching is not yielding much!
Thanks!

Best Answer

A =[ 3.0000    2.2200
  5.0000    2.2187
  7.0000    2.2171
  9.0000    2.2132
  11.0000    2.2168
  13.0000    2.2277
  15.0000    2.2283
  19.0000    2.2451];
a=A(1,:);
b=A(2:end,1);
k=1;
jj=1;
idx=[];
while k<=numel(b)
  f(jj)=b(k);
  if sum(f(1:jj))>=20
      idx(end+1)=k;
      jj=1;
     else
      jj=jj+1;
  end
  k=k+1;
end
out=[a;A(idx+1,:)]
I'am not sure if this is efficient for big matrices
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