Extrap: added note at end of Householder reflection algo

Research/Extrapolation methods/Code/ALGO_extrap_MPE_v3_20211119.m

@@ -19,3 +19,7 @@ for i=1:min(d,k)
     end
 end
 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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