function  [h, compUp] =  lfmComputeH4(gamma1_p, gamma1_m, sigma2, t1, preFactor, preExp,...
    mode, term )

% LFMCOMPUTEH4 Helper function for computing part of the LFM kernel.
%
%	Description:
%
%	H = LFMCOMPUTEH4(GAMMA1, GAMMA2, SIGMA2, T1, T2, MODE) computes a
%	portion of the LFM kernel.
%	 Returns:
%	  H - result of this subcomponent of the kernel for the given
%	   values.
%	 Arguments:
%	  GAMMA1 - Gamma value for first system.
%	  GAMMA2 - Gamma value for second system.
%	  SIGMA2 - length scale of latent process.
%	  T1 - first time input (number of time points x 1).
%	  T2 - second time input (number of time points x 1).
%	  MODE - indicates in which way the vectors t1 and t2 must be
%	   transposed
%	
%	
%	
%	
%	
%
%	See also
%	LFMKERNPARAMINIT, LFMXLFMKERNCOMPUTE


%	Copyright (c) 2007 David Luengo
%	Copyright (c) 2008 Mauricio Alvarez


%	With modifications by Neil D. Lawrence 2007
% 	lfmComputeH4.m SVN version 285
% 	last update 2011-06-16T07:23:44.000000Z

% Evaluation of h

if nargin<8
    term =[];
end

if ~mode
    if ~term
        if nargout>1
            compUp = lfmComputeUpsilonVector(gamma1_p,sigma2, t1);
            h = compUp*( preExp/preFactor(1) - conj(preExp)/preFactor(2)).';
        else
            h = lfmComputeUpsilonVector(gamma1_p,sigma2, t1)*( preExp/preFactor(1) - conj(preExp)/preFactor(2)).';
        end
    else
        if nargout>1
            compUp = lfmComputeUpsilonVector(gamma1_p,sigma2, t1);
            h = compUp*(preExp/preFactor(1)).' - conj(compUp)*(preExp/preFactor(2)).';
        else
            upsilon = lfmComputeUpsilonVector(gamma1_p,sigma2, t1);
            h = upsilon*(preExp/preFactor(1)).' - conj(upsilon)*(preExp/preFactor(2)).';
        end
    end
else
    if nargout > 1
        compUp{1} = lfmComputeUpsilonVector(gamma1_p,sigma2, t1);
        compUp{2} = lfmComputeUpsilonVector(gamma1_m,sigma2, t1);
        h =  compUp{1}*( preExp(:,1)/preFactor(1) - preExp(:,2)/preFactor(2)).' ...
            + compUp{2}*( preExp(:,2)/preFactor(3) - preExp(:,1)/preFactor(4)).';
    else
        h =  lfmComputeUpsilonVector(gamma1_p,sigma2, t1)*( preExp(:,1)/preFactor(1) - preExp(:,2)/preFactor(2)).' ...
            + lfmComputeUpsilonVector(gamma1_m,sigma2, t1)*( preExp(:,2)/preFactor(3) - preExp(:,1)/preFactor(4)).';
    end
end