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Discrete-time, second-order section, direct-form II transposed filter

`Hd = dfilt.df2sos(s)Hd = dfilt.df2tsos(b1,a1,b2,a2,...)Hd = dfilt.df2tsos(...,g)Hd = dfilt.df2tso`

`Hd = dfilt.df2sos(s)`
returns a discrete-time, second-order section, direct-form II, transposed
filter, `Hd`, with coefficients given in the `s` matrix.

`Hd = dfilt.df2tsos(b1,a1,b2,a2,...)` returns
a discrete-time, second-order section, direct-form II, tranposed filter, `Hd`,
with coefficients for the first section given in the `b1` and `a1` vectors,
for the second section given in the `b2` and `a2` vectors,
etc.

`Hd = dfilt.df2tsos(...,g)`
includes a gain vector `g`. The elements of `g` are
the gains for each section. The maximum length of `g` is
the number of sections plus one. If `g` is not specified,
all gains default to one.

`Hd = dfilt.df2tso` returns
a default, discrete-time, second-order section, direct-form II, transposed
filter, `Hd`. This filter passes the input through
to the output unchanged.

The resulting filter states column vector is

Specify a second-order sections, direct-form II, transposed discrete-time filter with coefficients from a sixth order, lowpass, elliptical filter using the following code:

[z,p,k] = ellip(6,1,60,.4); % Obtain filter coefficients [s,g] = zp2sos(z,p,k); % Convert to SOS Hd = dfilt.df2tsos(s,g)

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