Since samples of s1w and s2w are not exactly equal, you will need to define a tolerance value to find the point of intersection i.e. how much difference between value can still be treated as equal. In this case, following is one of the possible solutions
tol < 0.1; % change tolerance as required.
index = abs(s1w-s2w) < tol;
indexNumeric = find(index);
this will give you index from both vectors where values are almost equal.
