function [j, a,b,c,d, ierr] = evalB(t,x);
%
%     Evaluates Bsplines at value t in the interval
%     [x(1) : x(n)] with equally spaced points x(j)
%
      n = length(x);
      ierr = 0;

      if (t < x(1) | t > x(n)), ierr = 1; return; end

      h = x(2) - x(1);

      j = 1;
      while (t >  x(j)), j = j+1; end
      if(j > 1), j = j - 1; end
%
%     t is in [x(j),x(j+1))
%
%     evaluate  the four B_k(t) values that
%     are nonzero on this interval
%

      z = (x(j+1) - t)/h;
      a = z^3;
      b = 1 + 3*z + 3*z^2 - 3*z^3;

      z = (t - x(j))/h;
      c = 1 + 3*z + 3*z^2 - 3*z^3;
      d = z^3;