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// Copyright (C) 2018 - IIT Bombay - FOSSEE
// This file must be used under the terms of the CeCILL.
// This source file is licensed as described in the file COPYING, which
// you should have received as part of this distribution. The terms
// are also available at
// http://www.cecill.info/licences/Licence_CeCILL_V2-en.txt
// Author: Abinash Singh Under FOSSEE Internship
// Modifieded by: Abinash Singh Under FOSSEE Internship
// Last Modified : 3 Feb 2024
// Organization: FOSSEE, IIT Bombay
// Email: toolbox@scilab.in
function [s,g] = cell2sos(c)
// Calling Sequence :
// sos = cell2sos(cll)
// [sos,g] = cell2sos(cll)
// Description
// sos = cell2sos(cll) generates a matrix sos containing the coefficients of the filter system described by the second-order section cell array cll.
// [sos,g] = cell2sos(cll) also returns the scale gain g.
// Second-order section cell-array representation, specified as a cell array.
// Input Argument:
// For a filter system with L sections, specify 'cll' using this structure:
// * Cell array with L elements — For unity-gain filter systems. Each element of the cell
// array corresponds to a second-order section. The kth cell array element of 'cll'
// cll{k} = {[b_0k b_1k b_2k] [1 a_1k a_2k]}
// contains the coefficients from the kth second-order-section of the filter system H(z):
// H(z) = product(k=1 to L) H_k(z)
// = product(k=1 to L) (b_0k + b_1k*z^(-1) + b_2k*z^(-2))/(1 + a_1k*z^(-1) + a_2k*z^(-2))
// * Cell array with L+1 elements — If the gain of the filter system is different from 1.
// The first element of 'cll' contains the system gains at the numerator (g_n) and at
// the denominator (g_d). Then, the function appends each element of the cell array for
// the corresponding second-order section.
// The first and the k+1th cell array element of 'cll'
// cll{1} = {g_n g_d}
// cll{k+1} = {[b_0k b_1k b_2k] [1 a_1k a_2k]}
// contain the system gain and the coefficients from the kth second-order section of
// the filter system H(z), respectively, such that:
// H(z) = (g_n/g_d) * product(k=1 to L) H_k(z)
// = (g_n/g_d) * product(k=1 to L) (b_0k + b_1k*z^(-1) + b_2k*z^(-2))/(1 + a_1k*z^(-1) + a_2k*z^(-2))
// Output Argument:
// Second-order section representation, returned as an L-by-6 matrix, where L is the
// number of second-order sections. The matrix
// sos = [b_01 b_11 b_21 1 a_11 a_21]
// [b_02 b_12 b_22 1 a_12 a_22]
// [ ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ ]
// [b_0L b_1L b_2L 1 a_1L a_2L]
// represents the second-order sections of H(z):
// H(z) = g * product(k=1 to L) H_k(z)
// = g * product(k=1 to L) (b_0k + b_1k*z^(-1) + b_2k*z^(-2))/(1 + a_1k*z^(-1) + a_2k*z^(-2))
//
if(argn(2)~=1) then
error("cell2sos: Wrong number of input arguments");
end
L=prod(size(c));
k=1
for i=1:L
if(type(c(i))~=17)
error('cell2sos: Cell contents must themselves be cell objects');
end
end
gain_p = 0
if length(cell2mat(c{1}))== 2 then
gain_vec=cell2mat(c{1})
k=gain_vec(1)/gain_vec(2)
L=L-1
gain_p=1
end
s = zeros(L,6);
for i=1:L
if gain_p
s(i,:)=cell2mat(cll{i+1})
else
s(i,:)=cell2mat(cll{i})
end
end
if nargout < 2 then
s(1,1:3)= k * s(1,1:3)
else
g=k;
end
endfunction
/*
cll = {{[3 6 7] [1 1 2]}
{[1 4 5] [1 9 3]}
{[2 7 1] [1 7 8]}};
sos = cell2sos(cll) // passed
cll = {{1 2} {[3 6 7] [1 1 2]}
{[1 4 5] [1 9 3]}
{[2 7 1] [1 7 8]}};
sos = cell2sos(cll) // passed
*/
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