function write_dem(filename, DEM, xllcorner, yllcorner, cellsize, nodata)
% read_dem(filename, dlm) outputs a DEM and a DEM with NaN values from an
% ASCII file exported from ArcGIS
%        filename = 'filename.txt'
%         dem = matrix to be made into ascii file
%         xllcorner = lower left corner in x (I use UTM, but I think
%         longitude would work)  
%         yllcorner = lower left corner in y (I use UTM, but I think
%         latitude would work, too)  
%         cellsize = distance between grid/matrix points (m)
%         nodata = the integer that is represents no data (uses -9999 if
%         NaN is entered)  

% Format of text files
% % % % % % % % % % % % % % % % % % % % % % % % % % % % % 
% ncols m
% nrows n
% xllcorner 502035
% yllcorner 6622425
% cellsize 30
% NODATA_value -9999
% row 1 col1 [space] col2 [space]... colm [space-return]
% row 2 data [space-return]
% ...
% ...
% ...
% row n data [space-return]
% % % % % % % % % % % % % % % % % % % % % % % % % % % % % 

% Does the matrix have nan values?
if isnan(nodata) == 1
    nodata = -9999;
    DEM(find(isnan(DEM)==1)) = -9999;
end

% Define the different values to be used
[num(2), num(1)] = size(DEM);
num(3) = xllcorner;
num(4) = yllcorner;
num(5) = cellsize;
num(6) = nodata;

% define strings for headings
str{1} = ['ncols'];
str{2} = ['nrows'];
str{3} = ['xllcorner'];
str{4} = ['yllcorner'];
str{5} = ['cellsize'];
str{6} = ['NODATA_value'];

% make a file with the proper text values and such
fid = fopen(filename,'wt');
for j = 1:1:6
    if j == 1 || j == 2 || j == 6  
        fprintf(fid, '%s %d\n', str{j}, num(j));    % put in as integers
    else
        fprintf(fid, '%s %f\n', str{j}, num(j));
    end
end
fclose(fid);

% Write DEM into the proper format (flipud first)
DEMud = flipud(DEM);
dlmwrite(filename, DEMud, '-append','delimiter', ' ', 'precision', '%.4f', 'newline', 'pc')
% this uses 4 decimal places