# IIR_Butterworth_CS_Library 1.0.5

C# Library to calculate the coefficients of the Butterworth filter and to filter the data

This code calculates the coefficients of the Band-pass, Band-stop, Low-pass and High-pass Butterworth filters. It also filters the data, but no zero-phase delay is applied.

Each filter function will return a 2 rows x N coefficients 2D vector, where Row 1 = Numerator and Row 2 = Denumerator. The method "Check_stability_iir" can be used to check the stability of the filter. Please, keep in mind that if the filter is unstable, numerical instability leading to numerical overflow might happen when when the order selected is extremely high. If that situation occurs, the program might assign a default value of 10^10 at the denominator.

Band-pass: the function is "double[][] Lp2bp(double W_f1, double W_f2, int order_filt)". The first two arguments are the normalized two cut-off frequencies (f1/SF, f2/SF), which means that the cutoff frequencies must be within the interval of (0,1) and the last argument is the order;

Band-stop: the function is "double[][] Lp2bs(double W_f1, double W_f2, int order_filt)". The first two arguments are the normalized two cut-off frequencies (f1/SF, f2/SF), which means that the cutoff frequencies must be within the interval of (0,1) and the last argument is the order;

Low-pass: the function is "double[][] Lp2hp(double W_f1, int order_filt)". The first argument is the normalized two cut-off frequencies (f/SF), which means that the cutoff frequency must be within the interval of (0,1). The last argument is the order;

High-pass: the function is "double[][] Lp2lp(double W_f1, int order_filt)". The first argument is the normalized two cut-off frequencies (f/SF), which means that the cutoff frequency must be within the interval of (0,1). The last argument is the order;

Check the stability of the filter: the method is "bool Check_stability_iir(double[][] coeff_filt)". The argument is the 2D array containing the filter coefficients. It returns "true" if the filter is stable, "false" if it is unstable.

Filter the data: the method is "double[] Filter_Data(double[][] coeff_filt, double[] pre_filt_signal)". The two arguments are the filter coefficients and the signal to be filtered. It returns the filtered signal.

`Install-Package IIR_Butterworth_CS_Library -Version 1.0.5`
`dotnet add package IIR_Butterworth_CS_Library --version 1.0.5`
`<PackageReference Include="IIR_Butterworth_CS_Library" Version="1.0.5" />`
For projects that support PackageReference, copy this XML node into the project file to reference the package.
`paket add IIR_Butterworth_CS_Library --version 1.0.5`

## Used By

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