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Transform lowpass analog filters to highpass

`[bt,at] = lp2hp(b,a,Wo)[At,Bt,Ct,Dt] = lp2hp(A,B,C,D,Wo)`

`lp2hp` transforms analog lowpass filter prototypes
with a cutoff angular frequency of 1 rad/s into highpass
filters with desired cutoff angular frequency. The transformation
is one step in the digital filter design process for the `butter`, `cheby1`, `cheby2`, and `ellip` functions.

The `lp2hp` function 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] = lp2hp(b,a,Wo)` transforms an analog
lowpass filter prototype given by polynomial coefficients into a highpass
filter with cutoff angular frequency

Scalar `Wo` specifies the cutoff angular frequency
in units of radians/second. The frequency transformed filter is returned
in row vectors `bt` and `at`.

`[At,Bt,Ct,Dt] = lp2hp(A,B,C,D,Wo)` converts the continuous-time
state-space lowpass filter prototype in matrices

into a highpass filter with cutoff angular frequency `Wo`.
The highpass filter is returned in matrices `At`, `Bt`, `Ct`, `Dt`.

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