module igrad1 {	                                   # gradient in one dimension
#%  _lop( xx,  yy)
integer i
do i= 1, size(xx)-1 {
        if( adj) {
                xx(i+1) = xx(i+1) + yy(i)	   # resembles equation (1.2)
                xx(i  ) = xx(i  ) - yy(i)
		}
	else
                yy(i) = yy(i) + xx(i+1) - xx(i)	   # resembles equation (1.1)
	}
}