Question

The following code executes seemlessly

wave = HaarWavelet[];
type = "PrimalLowpass";

h = WaveletFilterCoefficients[
  wave, type, 
  WorkingPrecision -> \[Infinity]
];

h = Flatten[
    Take[h, 
        Range[1, Length[h]], 
        Table[2, {Length[h]}]
        ]
    ]

But when wrapping it with in a Module some goes awry. Consider the function

    getWaveletFilter[wave_, type_]:=
    Module[{filter}, (* treated as local *)
      filter = WaveletFilterCoefficients[
        wave, type, WorkingPrecision -> \[Infinity]
      ]

      filter = Flatten[
          Take[filter, 
              Range[1, Length[filter]], 
              Table[2, {Length[filter]}]
              ]
          ]

      filter
    ]

I would like getWaveletFilter[HaarWavelet[], "PrimalHighpass"]
to return

{1/2, -1/2}

Instead Mathematica, has all sorts of complains. Any suggestion?

Answer 1

You need to put a semi-colon between each action in your module to separate them:

getWaveletFilter[wave_, type_]:=
Module[{filter}, (* treated as local *)
  filter = WaveletFilterCoefficients[
    wave, type, WorkingPrecision -> \[Infinity]
  ];

  filter = Flatten[
      Take[filter, 
          Range[1, Length[filter]], 
          Table[2, {Length[filter]}]
          ]
      ];

  filter
]

Read CompoundExpression (;) for a better understanding.