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rINSTCONTROL/Utility functions/Initial parameter estimation/initParamDblLorentzian.m
03a4873e2235TekRSA-Freq-vs-Time

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initParamDblLorentzian.m
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function [p_in,lim_lower,lim_upper]=initParamDblLorentzian(x,y)
%Assumes form a/pi*b/2/((x-c)^2+(b/2)^2)+d/pi*e/2/((x-f)^2+(e/2)^2))+g
lim_upper=[Inf,Inf,Inf,Inf,Inf,Inf,Inf];
lim_lower=[-Inf,0,-Inf,-Inf,0,-Inf,-Inf];
%Finds peaks on the positive signal (max 2 peaks)
[~,locs{1},widths{1},proms{1}]=findpeaks(y,x,...
'MinPeakDistance',0.01*range(x),'SortStr','descend','NPeaks',2);
%Finds peaks on the negative signal (max 2 peaks)
[~,locs{2},widths{2},proms{2}]=findpeaks(-y,x,...
'MinPeakDistance',0.001*range(x),'SortStr','descend','NPeaks',2);
%If the prominence of the peak in the positive signal is greater, we adapt
%our limits and parameters accordingly, if negative signal has a greater
%prominence, we use this for fitting.
if isempty(proms{2}) || proms{1}(1)>proms{2}(1)
ind=1;
lim_lower(1)=0;
lim_lower(4)=0;
p_in(7)=min(y);
else
lim_upper(1)=0;
lim_upper(4)=0;
ind=2;
p_in(7)=max(y);
proms{2}=-proms{2};
end
p_in(2)=widths{ind}(1);
%Calculates the amplitude, as when x=c, the amplitude is 2a/(pi*b)
p_in(1)=proms{ind}(1)*pi*p_in(2)/2;
p_in(3)=locs{ind}(1);
if length(locs{ind})==2
p_in(5)=widths{ind}(2);
p_in(4)=proms{ind}(2)*pi*p_in(5)/2;
p_in(6)=locs{ind}(2);
else
p_in(5)=widths{ind}(1);
p_in(4)=proms{ind}(1)*pi*p_in(5)/2;
p_in(6)=locs{ind}(1);
end
%If one of the lorentzians is found to be much smaller than the other, we
%instead fit using only the greater lorentzian's parameters. This is an
%adaption for very closely spaced lorentzians.
if abs(p_in(1))>abs(10*p_in(4))
p_in(1)=p_in(1)/2;
p_in(5)=p_in(2);
p_in(6)=p_in(3);
p_in(4)=p_in(1);
end
lim_lower(2)=0.01*p_in(2);
lim_upper(2)=100*p_in(2);
lim_lower(5)=0.01*p_in(5);
lim_upper(5)=100*p_in(5);
end
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