function k = findint(nodes,x)
% Input: vector of nodes (of x-values)
%      : a value of x 
% Output: The subinterval index in which x lies. 
%         Interval numbering starts at 1. 


 if x<min(nodes) | x>max(nodes)
    disp('trying to interpolate outside of subdomains');
    disp('generated in findint.m');
    k = 0;
else
    testvec = x < nodes;
    [value,index] = max(testvec);
    k = index-1;
    if value <= 0
        k = length(testvec)-1;
    end
end