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 [b,a]=butter(6,0.01,'high');
 a

a =

  Columns 1 through 4 

   1.00000000000000  -5.87861915966800  14.40044053030134 -18.81528973284136

  Columns 5 through 7 

  13.82942473989109  -5.42164649008796   0.88569011331011

 b

b =

  Columns 1 through 4 

   0.94111110572031  -5.64666663432186  14.11666658580466 -18.82222211440621

  Columns 5 through 7 

  14.11666658580466  -5.64666663432186   0.94111110572031

 [b,a]=butter(6,0.002,'high');
 a

a =

  Columns 1 through 4 

   1.00000000000000  -5.97572364399462  14.87891271530635 -19.75841215795479

  Columns 5 through 7 

  14.75899663355906  -5.87978943446851   0.97601588755256

 b

b =

  Columns 1 through 4 

   0.98793516363806  -5.92761098182836  14.81902745457091 -19.75870327276121

  Columns 5 through 7 

  14.81902745457091  -5.92761098182836   0.98793516363806

 