combination function using ndgrid

Hello,

I want to build a function which use ndgrid.

My function is

function [ varargout ] = comb( varargin )

[varargout]=ndgrid(varargin)

varargout=varargout(:);

disp([varargout])

end

My varargout are x1 x2 x3 and varargin are a,b,c where a=[1 2], b=[2 3] and c=[1 4]. Expected results are

       1     2     1

       2     2     1

       1     3     1

       2     3     1

       1     2     4

       2     2     4

       1     3     4

       2     3     4

but it seems like ndgrid doesn't work. What can i do? In command window works fine but as a function where I can put more varargins something is wrong.

Answer 1

[Guillaume]

function varargout = comb(varargin)
   varargout = cell(1, nargout);
   [varargout{:}] = ndgrid(varargin{:};  %distribute to varargout
   varargout = cellfun(@(m) reshape(m, [], 1), varargout, 'UniformOutput', false); %reshape into columns
end

[Nik Sam]

Now is this

[x1,x2,x3]=comb(a,b,c)

x1 =

     1
     2
     1
     2
     1
     2
     1
     2

x2 =

     2
     2
     3
     3
     2
     2
     3
     3

x3 =

     1
     1
     1
     1
     4
     4
     4
     4

[Guillaume]

So do you want one output as a matrix, or a variable number of outputs as vectors?

If you just want one output as a matrix, then you misled us with your varargout and the function is simply:

function c = comb(varargin)
   c = cell(size(varargin));
   [c{:}] = ndgrid(varargin{:};
   c = cell2mat(cellfun(@(m) reshape(m, [], 1), c, 'UniformOutput', false)); %reshape into columns and convert to matrix
end

[Nik Sam]

I want a variable number of outputs because I want after that to compute equation like that

a=[1 2], b=[2 3], c=[1 4] so I want first the combination like

[x1 x2 x3] = comp(a,b,c) to give this:

       1     2     1
       2     2     1
       1     3     1
       2     3     1
       1     2     4
       2     2     4
       1     3     4
       2     3     4

and after to compute the equation F=x1*(x2-x3) like 1*(2 -1)=1, 2*(2-1)=2 etc.

Is there another way to achieve this? I dont know..

[Guillaume]

What you are saying makes no sense. You say you want three outputs (x1, x2, and x3) and then show what looks like a single matrix.

The x1, x2, and x3 returned by my first function are the columns of that matrix. The matrix returned by second function is that matrix.

You can use either form to calculate your F:

%using variable number of outputs:
[x1, x2, x3] = comb(a, b, c); %1st version of comb
F = x1 .* (x2 - x3)

%using single output:
x123 = comb(a, b, c); %2nd version of comb
F = x123(:, 1) .* (x123(:, 2) - x123(:, 3))

[Nik Sam]

thanks a lot man

But the best of all it will be to have the following:

[x1 x2 x3] = comb(a,b,c)

       1     2     1
       2     2     1
       1     3     1
       2     3     1
       1     2     4
       2     2     4
       1     3     4
       2     3     4

and after

F=x1.*(x2-x3)

T=min(F)

W=max(F)

IS THERE A WAY FOR THAT?

[Nik Sam]

function  varargout  = comb( varargin )

varargout = cell(1, nargout);

     [varargout{:}] = ndgrid(varargin{:});  %distribute to varargout

    varargout = cell2mat(cellfun(@(m) reshape(m, [], 1), varargout, 'UniformOutput', false)); %reshape into columns

end

something like this but it doesnt work

[Guillaume]

I'll say again: "What you are saying makes no sense. You say you want three outputs (x1, x2, and x3) and then show what looks like a single matrix".

You can of course concatenate the 3 outputs for display. Using the varargout form of comb:

[x1, x2, x3] = comb(a, b, c);
[x1, x2, x3]  %for display
F = x1 .* (x2 - x3)
T = min(F)
W = max(F)

[Nik Sam]

Can I have that display form directly inside the function comb?

Maybe something like

[varargout];

celldisp[varargout];

But it doesnt work like that.

THIS IS MY LAST QUESTION..

[Guillaume]

[varargout{:}]

at the end of the function will do it. This will always display the output whether or not you terminate the call to comb with a semicolon, so I wouldn't recommend it.

There is no way to detect if a function has called with a semicolon or not, so you can't toggle that behaviour.

[Nik Sam]

Really thanks for your time my friend..Now finally I have the desired result..

Thanks again...

Answer 2

[Walter Roberson]

[varargout{:}] = ndgrid(varargin{:});

[Nik Sam]

I am trying to run this in command window like

a=[1,2];

b=[2,3];

c=[1,4];

[x1 x2 x3] = comp(a,b,c)

but I get this message

Expected one output from a curly brace or dot indexing expression, but there were 0 results.

Error in comp (line 3) [varargout{:}] = ndgrid(varargin{:});

[Walter Roberson]

function [ varargout ] = comb( varargin )
  [varargout{1:nargout}] = ndgrid(varargin{:});
end

[Nik Sam]

This works my friend but if I run the following

>> a=[1,2];

>> b=[2,3];

>> c=[1,4];

>> [x1,x2,x3]=comb(a,b,c)

I get this

x1(:,:,1) =

     1     1
     2     2

x1(:,:,2) =

     1     1
     2     2

x2(:,:,1) =

     2     3
     2     3

x2(:,:,2) =

     2     3
     2     3

x3(:,:,1) =

     1     1
     1     1

x3(:,:,2) =

     4     4
     4     4

But i want as result:

       1     2     1
       2     2     1
       1     3     1
       2     3     1
       1     2     4
       2     2     4
       1     3     4
       2     3     4

Answer 3

[Jos (10584)]

Take a look the content of ALLCOMB, which does exactly what you're after btw...

http://www.mathworks.com/matlabcentral/fileexchange/10064-allcomb-varargin-