function [A]=construct(t,tau)
    m = size(tau,1);
    n = size(t,1);
    A= zeros(m,n)
    for i = 1:m
        j = place(t, tau(i))
        A(i,j) = (tau(i)-t(j+1))/(t(j)-t(j+1))
        A(i,j+1) = (tau(i)-t(j))/(t(j+1)-t(j))
    end
endfunction