Extrap: added note at end of Householder reflection algo

Research/Extrapolation methods/Code/ALGO_extrap_MPE_v3_20211119.m

@@ -18,4 +18,8 @@ for i=1:min(d,k)
         r_out(i) = norm(F(:,1:i)*u);
     end
 end
-end
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+end
+
+% note: this is equivalent to previous formulation of HH reflections, with
+% no significant change in results; also, unsure how to apply GMRES for k
+% greater than d
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