MATLAB: Format data into string and write a txt file

formatMATLABnum2str

Hi,
I have the following cell,
a={[1E5 0 0 7.82E12 0]
 [-1 0 0 -1 0]};
and I want to write a text file with the following format
 1.0000000000000000E+05  0.0000000000000000E+00  0.0000000000000000E+00  7.8200000000000000E+12  0.0000000000000000E+00
-1.0000000000000000E+00  0.0000000000000000E+00  0.0000000000000000E+00 -1.0000000000000000E+00  0.0000000000000000E+00
As in two blank spaces at the beginning of the line if the first value is positive (line 1) and one blank space if it is negative (line 2), the "-" uses one space. There are also two blank spaces in between the values (if the value is negative the "-" uses one of those blank spaces).
First I tried converting a to a string cell:
for i=1:2
  a{i}=num2str(a{i},'%.16e');
end
And I get this:
a =
2×1 cell array
    {'1.0000000000000000e+050.0000000000000000e+000.0000000000000000e+007.8200000000000000e+120.0000000000000000e+00'     }
    {'-1.0000000000000000e+00 0.0000000000000000e+00 0.0000000000000000e+00-1.0000000000000000e+00 0.0000000000000000e+00'}
There are no blank spaces at all. Is it possible to specify the number of blank spaces in between the values?
Thank you,

Best Answer

A cell array of numeric vectors is quite inconvenient to work with, so the first thing to do is convert it to a much easier to use numeric matrix:
a = {[1E5,0,0,7.82E12,0],[-1,0,0,-1,0]};
m = vertcat(a{:});
Method one: dlmwrite:
dlmwrite('sample.txt', m, 'delimiter',' ', 'precision','% .16E')
Method two: fprintf:
fmt = repmat(' % .16E',1,size(m,2));
fmt = [fmt(2:end),'\n'];
fprintf(fmt,m.')
prints this:
 1.0000000000000000E+005  0.0000000000000000E+000  0.0000000000000000E+000  7.8200000000000000E+012  0.0000000000000000E+000
-1.0000000000000000E+000  0.0000000000000000E+000  0.0000000000000000E+000 -1.0000000000000000E+000  0.0000000000000000E+000
To write to a text file, add fopen and fclose:
[fid,msg] = fopen('sample.txt','wt');
assert(fid>=3,msg)
fprintf(fid,fmt,m.')
fclose(fid)
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