Unknown number of output variables

There are some functions that support variable number of output variables. For example, ind2sub(), depending on the matrix size, could have variable number of output.

if I type:

[I1,I2]=ind2sub([3,4],10);

I get the correct answer, I1=1 and I2=4;

but if I issue:

subIndices=ind2sub([3,4],10);

then I won't get subIndices= [1,4]; but I get subIndices=10; which definitely is not what I wanted.

Now here is my quesitons. What if I don't know the input size and that is defined during the runtime, meaning that my input size once might be [3,4] and another time it would be [3,4,5]. So once I need to call [I1,I2]=ind2sub([3,4],10) but another time I need to have [I1,I2,I3]=ind2sub([3,4,5],10) in the code.

In this easy case I just rewrote another version of ind2sub which outputs the indices as vector, you can see the code at the end of this post; but what is a better way of doing this?

P.S. I don't want to construct the command string and use eval()

Here is the modified version of ind2sub():

function subIndices = myInd2Sub(inputSize,index)
%%myInd2Sub is similar to MATLAB's ind2sub except that the output, i.e. 
%  the indices for each dimensions, are provided in a single array, instead
%  of separate output variables.

      % Checking input arguments
      validateattributes(inputSize, ...
                         {'numeric'}, ...
                         {'vector','integer','positive'});
      validateattributes(index, ...
                         {'numeric'}, ...
                         {'scalar','integer','positive','<=',prod(inputSize)});

      % preparing the output
      subIndices = zeros(numel(inputSize),1);

      % changing the index to zero-base
      index = index - 1;

      % calculating the indices for each dimension
      for i=numel(subIndices):-1:2
          nElem = prod(inputSize(1:i-1));
          subIndices(i) = floor(index/nElem);
          index = index - subIndices(i)*nElem;
      end
      subIndices(1) = index;

      % changing back the indices to 1-base.
      subIndices = subIndices + 1;
  end

Answer 1

[Steven Lord]

Use comma-separated lists (CSLs.)

 % User specifies number of inputs/outputs at runtime
 N = input('Enter number of dimensions to mesh (2-5) ');

 % Inputs to NDGRID specified at runtime by user as elements of a cell array
 inputs = repmat({[0,1]}, 1, N);

 % Outputs from NDGRID specified at runtime by user as elements of a cell array
 outputs = cell(1, N);

 % Call NDGRID with specified number of inputs and outputs by turning cell arrays into CSLs
 [outputs{:}] = ndgrid(inputs{:});

 % Use the outputs to display the coordinates of one of the points on the grid
 d = input(sprintf('Enter an integer value between 1 and %d ', 2^N));
 fprintf('Your combination is:')
 for k = 1:N
    fprintf(' %d', outputs{k}(d));
 end
 fprintf('\n')

I didn't add in any error checking for the values of N or d because this is a very quick example. But I wouldn't use too large an N as it could use a lot of memory.

[Mohammad Abouali]

Great. That's exactly what I wanted. Thanks.