FUN_nc_varget_sub_genStartCount.m

function [start, count, xloc] = FUN_nc_varget_sub_genStartCount( x, xlimit )
%  [start, count, xloc] = FUN_nc_varget_sub_genStartCount( x, xlimit )
%
% Generate [start, count] for FUN_nc_varget_enhanced_region(filename,varname,start,counts,stride)
% xloc is the location of selected x based on xlimit: x(xloc);
%
% V1.43 by L. Chi
%   Extend the feature introduced in v1.41
%   Even if x is not monotonic, a warning message, instead of an errow, will
%      be triggered if x is monotonic within `xlimit`
%   Like v1.41, this is introduced to override some bugs in HYCOM data (e.g, exp 93.0)
% V1.42 by L. Chi
%   Return an error if xlimit(1) > xlimit(2).
% V1.41 by L. Chi
%   if x is always within xlimit, ignore the monotonic check. 
%      This is introduced to read some of HYCOM datasets. (e.g., expt_93.0) 
% V1.40 by L. Chi
%   x & xlimit will be forced as double type
% V1.30 by L. Chi
%   Add support for decresing x 
% V1.20 by L. Chi
%   Fix a but: In the older version, this function will return 
%              start = 0, count = 1, xloc = 1 when x is completely out of
%              the range defined by xlimit. 
% V1.10 by L. Chi
%   Add support for -inf, inf in xlimit
%   Add monotone check.
%
% V1.00 by L. Chi (L.Chi.Ocean@outlook.com)

%%

% preparation: force x as double type
x = double(x);
xlimit = double(xlimit);

if isempty( xlimit )
    xlimit = [-inf inf];
end

if xlimit(1) > xlimit(2)
   error('xlimit(2) >= xlimit(1) is required for all dimensions!') 
end

%
if (  length(x) == 1  ) || all(  x(2:end)-x(1:end-1) > 0  )
    is_x_decrese = 0;
elseif all(  x(2:end)-x(1:end-1) < 0  )
    is_x_decrese = 1;
    x = x(end:-1:1);
else
   % the input x is not monotonic
   if all( x >= xlimit(1) & x <= xlimit(2)  )
       start = 0; % matrix begin with 0 in nc files.
       count = length(x);
       xloc = [1:length(x)];
       
       warning('x is not monotonic, however, data will still be loaded since the entire domain is within the required limit! Please be careful about the output' )
       return
   else
       
       ck_tem_ind = find( x >= xlimit(1) & x <= xlimit(2) );
       
       if all( diff(ck_tem_ind) == 1 ) 
           
           % Skip the error if the data is monotonic within the required limit.
           % This is introduced from reading HYCOM data (exp 93.0)
           
           %if all( diff( x(ck_tem_ind) ) > 0 )
           %     is_x_decrese = 0; 
           %elseif all( diff( x(ck_tem_ind) ) < 0 )
           %     is_x_decrese = 1;
           %     x = x(end:-1:1);
           %else
           %    error('Unexpected value!');
           %end
           
           if median( diff( x(ck_tem_ind) ) > 0 )
                is_x_decrese = 0;
           
           elseif median( diff( x(ck_tem_ind) ) < 0 )
                is_x_decrese = 1;
                x = x(end:-1:1);
           else
               error('Unexpected value!');
           end
           
           warning(['x is not monotonic, however, it is monotonic within the inquired limit! Plase check its raw values!']);
           
       else          
           % x must be monotonic within the required limit.
           error('x must be monotonic.');
       end
   end
end

% Get location of start
if isinf(xlimit(1))
    start_loc = 1;
else
    tem = ( x - xlimit(1) ); 
    tem( tem<0 ) = nan; 
    
    if all( isnan(tem) )
        % All x is smaller than xlimit(1)
        start_loc = nan;
    else
        % at least one x >= xlimit(1)
        [~, start_loc] = min(tem);
    end
        clear tem
end

% Get location of end
if isinf(xlimit(2))
    end_loc = length(x);
else
    tem2 = ( x - xlimit(2) ); 
    tem2( tem2>0 ) = nan; 
    
    if all(isnan( tem2 ))
        % all x is larger than xlimit(2)
        end_loc = nan;
    else
        % At least one x <= xlimit(2) 
        [~, end_loc] = max(tem2);
    end
        clear tem2
end

% 
if isnan( start_loc ) || isnan( end_loc )
    % x is completely out of the range defined by xlimit 
    start = nan;
    count = 0;
    xloc  = [];
else 
    % At least one x is located in [ xlimit(1),  xlimit(2)]
    start = start_loc - 1; % matrix begin with 0 in nc files. 
    count = end_loc - start_loc + 1;
    xloc = start_loc:end_loc;
end


% additional steps for decreasing x ---------------------------------------
if is_x_decrese == 1
    start =  length(x) - end_loc  ;
    xloc  = start+1 : start+count;
end
% -------------------------------------------------------------------------

return