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It's a beginner question, but useful to users from python - signal.lfilter, I was using lfilter from Find reverse one pole lowpass filter

The doubt now is, how to rewrite the iir filter to 'revert' the low pass filter, without using lfilter function:

low pass:

y[i] = y[i-1] * 0.8702 + x[i] * 0.1298
y[i] = signal.lfilter(b,a,x)

low pass revert:

y[i] = y[i-1] * ?? + x[i] * ?? + ??
y[i] = signal.lfilter(a,b,x)
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from:

a[0]*y[n] = b[0]*x[n] + b[1]*x[n-1] + ... + b[M]*x[n-M]
                      - a[1]*y[n-1] - ... - a[N]*y[n-N]

rewrite to:

a=[0.1298]
b=[1,-.8702]

a[0] * y[n] = b[0] * x[n] + b[1] * x[n-1]

y[n] = ( 1 * x[n] + -.8702*x[n-1] )/.1298
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