function [Isext,GL]=get_ATF2_sexts_I(KL,energy,fflag)
%
% [Isext,GL]=get_ATF2_sexts_I(KL,energy,fflag);
%
% Compute ATF2 sext currents from KLs and beam energy
%
% INPUTS:
%
%   KL     = sext KLs (1/m^2) [5 element array]
%   energy = beam energy (GeV)
%   fflag  = (optional) if present and zero, fudge factors will not be used
%
%   The order of sextupole currents must be:
%
%    SF6FF,SF5FF,SD4FF,SF1FF,SD1FF
%
% OUTPUTS:
%
%   Isext = ATF2 sext currents (amps)
%   GL    = integrated sext strengths (kG/m)

Nsext=5;

% check input args

if (nargin<2)
  error('At least 2 input arguments required')
end
if (length(KL)~=Nsext)
  error('Incorrect KL length')
end
if (energy<=0)
  error('Bad energy value')
end
if (nargin==2)
  fudge=1;
else
  fudge=(fflag~=0);
end

% ==============================================================================
%
% ATF2 SEXTUPOLE MAGNET DATA
%
% ==============================================================================

% there are 2 types of ATF2 sextupole:

%    1 = 1.625SX3.53 (SLC)
%    2 = 2.13S3.00 (FFTB)

r0=[0.020638;0.02705];      % poletip radius (m)
sleff=[0.32834*0.3048;0.1]; % effective length (m)

% MMS data for sext types (I is amp, B is T @ r0)
% (from: SLC FF "SX3" polynomials
%        ATF$MAG:MAG_KI_S_SLAC_213.FOR)

Nmms=[6;21];
sI=[ ...
   0.0, 0.0; ...
  10.0, 0.5; ...
  20.0, 1.0; ...
  30.0, 1.5; ...
  40.0, 2.0; ...
  50.0, 2.5; ...
   0  , 3.0; ...
   0  , 3.5; ...
   0  , 4.0; ...
   0  , 4.5; ...
   0  , 5.0; ...
   0  , 5.5; ...
   0  , 6.0; ...
   0  , 6.5; ...
   0  , 7.0; ...
   0  , 7.5; ...
   0  , 8.0; ...
   0  , 8.5; ...
   0  , 9.0; ...
   0  , 9.5; ...
   0  ,10.0; ...
];
     
sB=[ ...
  0.000000,0.000000; ...
  0.051997,0.004694; ...
  0.100725,0.010154; ...
  0.149881,0.015612; ...
  0.199296,0.021068; ...
  0.248563,0.026522; ...
  0       ,0.031973; ...
  0       ,0.037422; ...
  0       ,0.042868; ...
  0       ,0.048312; ...
  0       ,0.053753; ...
  0       ,0.059190; ...
  0       ,0.064624; ...
  0       ,0.070054; ...
  0       ,0.075480; ...
  0       ,0.080900; ...
  0       ,0.086314; ...
  0       ,0.091722; ...
  0       ,0.097121; ...
  0       ,0.102511; ...
  0       ,0.107890; ...
];
    
% sextupole types and polarities

stype=[1,1,1,2,2];
ssgn=[+1,-1,+1,-1,+1];

% "Kubo" fudge factors
% (none defined at this time ... )

sfudge=zeros(Nsext,1);

% ==============================================================================

% compute rigidity

Cb=1e10/2.99792458e8; % kG-m/GeV
brho=Cb*energy;

% compute sextupole strengths
% (NOTE: polynomial evaluation is not presently used to convert current
%        to gradient ... linear interpolation of MMS data is used)

GL=zeros(Nsext,1);
Isext=zeros(Nsext,1);
for n=1:Nsext
  if (KL(n)==0)
    GL(n)=0;
    Isext(n)=0;
  else
    GL(n)=brho*KL(n); % kG/m
    nt=stype(n);
    B=0.5*brho*KL(n)*r0(nt)^2/sleff(nt); % kG
    B=0.1*B; % T
    if (fudge),B=B*(1+sfudge(n));end % apply the fudge factor
    Isext(n)=interp1(sB(1:Nmms(nt),nt),sI(1:Nmms(nt),nt),abs(B),'linear');
  end
end