creating strings with variables

I have to access many different files with slightly different names and instead of manually writing them in matlab I want to dynamically create them. So I have:

 mat_frac = zeros(21,21);
 mat_Tp   = zeros(21,21);
 for i=1:21
    for j=1:21
        mat_frac(i,j)=i*0.0005;
        mat_Tp(i,j)=1290+j*10;
    end
 end
 mat_frac(end,:)=1.000;
 mat_frac = mat_frac(:);
 mat_Tp   = mat_Tp(:);

 for i=1:numel(mat_frac)
   evalit = sprintf('file{%d}=nuPots_run1_120_1cm_%d_%1.3ffrac_h1_100km_0block_1salters_1mpyr_10dV;',i,mat_Tp(i),mat_frac(i));
   eval(evalit);
 end

But this does not work because I get the attempted operation:

file{1}=nuPots_run1_120_1cm_1300_0.001frac_h1_100km_0block_1salters_1mpyr_10dV;

instead of the correct:

file{1}='nuPots_run1_120_1cm_1300_0.001frac_h1_100km_0block_1salters_1mpyr_10dV';

But I cannot add the relevant apostrophe's in the sprintf line. So how do I correct this?

Answer 1

[per isakson]

This code is much more complicated than needed.

 for i=1:numel(mat_frac)
   evalit = sprintf('file{%d}=nuPots_run1_120_1cm_%d_%1.3ffrac_h1_100km_0block_1salters_1mpyr_10dV;',i,mat_Tp(i),mat_frac(i));
   eval(evalit);
 end

• No need to use eval! It makes debugging difficult and more reason are available in the FAQ. And counting blips is error prone.
• Are you sure all meta data must be squeezed into the filename?
• Do you really want "random" dots in the filename?

Try something like

   file{ii} = sprintf('nuPots_run1_120_1cm_%d_%1.3ffrac_..._10dV'  ... 
                    ,  mat_Tp(ii), mat_frac(ii)                    );

"But I cannot add the relevant apostrophe's in the sprintf line." &nbsp Do you want the filename to begin and end with an apostrophe? Isn't the value of file{ii} supposed to be a text string without enclosing blips?

Answer 2

[Guillaume]

To add apostrophes to a string, you just double them:

s = 'some string with an apostrophe here -> '' <- and here -> '' <-';

As per isakson said, your whole code is very inefficient. I particularly don't understand why you went with eval. Get into the habit of never using eval. 99.9% of the time there's a more efficient way. Also, your first two loops are completely unnecessary:

[i, j] = ndgrid(1:21, 1:21);
mat_frac = i * 0.0005;
mat_Tp = 1290 + 10 * j;
mat_frac(end, :) = 1;

You also don't need to reshape (with (:)) your matrices if you're using linear indexing:

files = cell(1, numel(mat_frac);
for fidx = 1:numel(mat_frac)
  files{fidx} = sprintf('nuPots_run1_120_1cm_%d_%1.3ffrac_h1_100km_0block_1salters_1mpyr_10dV', mat_Tp(fidx), mat_frac(fidx));
end

Or you could use arrayfun to replace the loop:

files = arrayfun(@(t,f) sprintf('nuPots_run1_120_1cm_%d_%1.3ffrac_h1_100km_0block_1salters_1mpyr_10dV', t, f), mat_Tp(:), mat_frac(:), 'UniformOutput', false); %and no need to predeclare files.