function yval = recursive_legendre ( k , xval )
  if k<0
    error('recursive_legendre: k must be nonnegative.');
  elseif k==0
    yval = ones(size(xval));
  elseif k==1
    yval = xval;
  else
    yval = ((2*k-1)*xval.*recursive_legendre(k-1,xval) ...
            - (k-1)*recursive_legendre(k-2,xval) )/k;
  endif
endfunction