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//Author: Parthasarathi Panda
//parthasarathipanda314@gmail.com
function typ=firtype(b)
//This function identifies Type of linear phase FIR filter
//Calling Sequence
//t = firtype(b)
//Parameters
//t: type of an FIR filter
//b: Filter coefficients
//Description
//t = firtype(b) determines the type, t, of an FIR filter with coefficients b. t can be 1, 2, 3, or 4. The filter must be real and have linear phase.
//Examples
//b=[9.2762e-05 9.5482e-02 4.0443e-01 4.0443e-01 9.5482e-02 9.2762e-05]
//firtype(b)
//Output : 2
//b=[-1 -2 0 2 1]
//firtype(b)
//Output : 3
if (type(b)~=1) then
error('check input type');
end
v=size(b);
if length(v)>2 then
error('check input dimension');
end
if v(1)~=1 & v(2)~=1 then
error('check input dimension');
elseif v(2)==1
b=b';
end
m=length(b);
sym=(b-b($:-1:1))*(b-b($:-1:1))';//zero if symmetrical
antisym=(b+b($:-1:1))*(b+b($:-1:1))';//zero if antisymmetrical
if (sym==0) then
if (pmodulo(m,2)==1) then
typ=1;
else
typ=2;
end
elseif (antisym==0)
if (pmodulo(m,2)==1) then
typ=3;
else
typ=4;
end
else
typ=-1;//not linear phas
end
endfunction
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