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Transform lowpass analog filters to bandpass

`[bt,at] = lp2bp(b,a,Wo,Bw)[At,Bt,Ct,Dt] = lp2bp(A,B,C,D,Wo,Bw)`

`lp2bp` transforms
analog lowpass filter prototypes with a cutoff angular frequency of
1 rad/s into bandpass filters with desired bandwidth
and center frequency. The transformation is one step in the digital
filter design process for the `butter`, `cheby1`, `cheby2`,
and `ellip` functions.

`lp2bp` can perform the transformation on two different linear system representations:
transfer function form and state-space form. In both cases, the input
system must be an analog filter prototype.

`[bt,at] = lp2bp(b,a,Wo,Bw)` transforms an analog
lowpass filter prototype given by polynomial coefficients into a bandpass
filter with center frequency

Scalars `Wo` and `Bw` specify
the center frequency and bandwidth in units of rad/s. For a filter
with lower band edge `w1` and upper band edge `w2`,
use `Wo` = `sqrt(w1`*`w2)` and `Bw` = `w2-w1`.

`lp2bp` returns the frequency transformed filter
in row vectors `bt` and `at`.

`[At,Bt,Ct,Dt] = lp2bp(A,B,C,D,Wo,Bw)` converts the
continuous-time state-space lowpass filter prototype in matrices

into a bandpass filter with center frequency `Wo` and
bandwidth `Bw`. For a filter with lower band edge `w1` and
upper band edge `w2`, use `Wo` = `sqrt(w1`*`w2)` and `Bw` = `w2-w1`.

The bandpass filter is returned in matrices `At`, `Bt`, `Ct`, `Dt`.

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