Here we do a crazy regression. It says: adjust the coefficients of the general quartic so that it passes through all both points, has derivative 0 at both points, and second derivative 0 at one of them
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式13: left bracket, "f" left parenthesis, "x" Subscript, 1 , Baseline , right parenthesis , "f" left parenthesis, "x" Subscript, 2 , Baseline , right parenthesis , "h" left parenthesis, "x" Subscript, 2 , Baseline , right parenthesis , "g" left parenthesis, "x" Subscript, 1 , Baseline , right parenthesis , "g" left parenthesis, "x" Subscript, 2 , Baseline , right parenthesis , right bracket tilde left bracket, "y" Subscript, 1 , Baseline , "y" Subscript, 2 , Baseline , 0 , 0 , 0 , right bracketfx1,fx2,hx2,gx1,gx2~y1,y2,0,0,0