function [A,B] = gradab(N)
% constrains a vector to be increasing w/jumps at most 1
A = zeros(0,N);
B = zeros(0,1);
rind = 0;
for i=1:N-1
    i1 = i;
    i2 = i+1;
    rind = rind + 1;
    A(rind,i2) = 1;
    A(rind,i1) = -1;
    B(rind,1) = 1;
    rind = rind + 1;
    A(rind,i2) = -1;
    A(rind,i1) = 1;
    B(rind,1) = 0;
end
return