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% find_om_grid.m: finds a suitably dense omega axis

% GUISDAP v.1.60 96-05-27 Copyright Asko Huuskonen and Markku Lehtinen

%

% The frequency axis (p_om) for the spectral ambiguity function is chosen so 

% that the spectral resolution is sufficent for all cases. Therefore the

% resolution is much too good when the spectrum is wide. This function checks

% the oversampling prior to data analysis and returns spectral ambiguity

% function and frequency axis  which are sufficient but not too good.

%

% See also: half_prof

%

% function [womega,om]=find_om_grid(p,f_womega,kd2,p_om,pldfvv)

function [womega,new_om]=find_om_grid(p,f_womega,kd2,p_om,pldfvv,nostep)



global p_m0



[nin0,tit0,mim0,psi,vi]=transf(p,p_m0);

s=spec(nin0,tit0,mim0,psi,vi,kd2,p_om,pldfvv);

[M,N]=size(f_womega);

N=floor(N/2)+1;



lenp=length(p_om);

start=1;

istep=1;

ii=[];

if ~nostep

  for i=2:(lenp-1)/2

    tii=(lenp-1)/i;

    if tii==fix(tii), ii=[ii i]; end

  end

end

for i=[1 ii]

  ind=[fliplr(N-i:-i:start) N:i:lenp-start+1];

  om=p_om(ind); len=length(om);

  dom=0.5*[om(2)-om(1);om(3:len)-om(1:len-2);om(len)-om(len-1)];

  theo=f_womega(:,ind)*(s(ind).*dom);

  if i==1

    theoref=theo;

  else

    err=max(abs(theoref-theo))/max(abs(theo));

%   fprintf(' step %.0f, error %.4f\n',i, err);

    if err>1.5e-3, break, end

  end

  istep=i; new_om=om; new_ind=ind; new_dom=dom';

end

%if istep>1, fprintf(' Using a coarser frequency axis, one of every %d point used\n',istep), end

womega=f_womega(:,new_ind).*new_dom(ones(M,1),:);