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Default

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Default[f]

gives the default value for an omitted parameter of f.

Default[f, k]

gives the default value for a parameter on the k-th position.

Default[f, k, n]

gives the default value for the k-th parameter out of n.

Assign values to Default to specify default values.

• • Default[f] = 1

• • f[x_.] := x ^ 2

• • f[]

Default values are stored in DefaultValues:

• • DefaultValues[f]

You can use patterns for k and n:

• • Default[h, k_, n_] := {k, n}

Note that the position of a parameter is relative to the pattern, not the matching expression:

• • h[] /. h[___, ___, x_., y_., ___] -> {x, y}