Converting binary like table but using decimal values

I'm trying to create a table that will start at a negative value and increment by one in the right most column and each column to the left will only increment when there is a carry. This is similar to a binary table or any other base-n table, but I would like to keep the values in decimal format, not alpha-numeric.

I had this code which was working well, but fails if I make 'n' > 5 due to the alpha-numerics once the decimal value reaches '10'.

m = 3;    %Number of signals
n = n+1;  %Number of harmonics

%% Harmonic Basis Matrix
T = zeros((2*n-1)^m,m);
for k = 1:(2*n-1)^m
    T(k,:) = dec2base(k-1,2*n-1,m)-num2str(n-1);
end

When I subtract num2str(n-1) from the string '00A', the result is double('00A') = 17 - double('0') = 5 ==> 17-5 = 12.

I thought about creating the matrix in alpha-numeric string form and just splitting the values into columns, but couldn't figure out how to do that effectively without using cells - which I need to avoid as this will be used in some matrix algebra.

Please note, that the variables 'm' and 'n' are part of a function input and could be completely arbitrary.

Thanks for the help!

[Jan]

Can you give us a short example for some inputs and outputs? I do not understand, what you are asking for.

[Kyle Young]

The inputs are quite simple in this case, m and n, where m is the number of columns in the matrix and n is the 'base'.

Basically, if I have 2 elements (m=2) and I would like to create a cross modulation table with 2 terms (n=2), I would get this result:

T =
    -2    -2
    -2    -1
    -2     0
    -2     1
    -2     2
    -1    -2
    -1    -1
    -1     0
    -1     1
    -1     2
     0    -2
     0    -1
     0     0
     0     1
     0     2
     1    -2
     1    -1
     1     0
     1     1
     1     2
     2    -2
     2    -1
     2     0
     2     1
     2     2

The hard part is when I have a large N term, which then produces A's and B's and C's during the dec2base(). Using this method I am also limited to an N value less than 36.

[Jan]

I assume, you mean (2*n+1)^m, not (2*n-1)^m.

[Stephen23]

>> [X,Y] = meshgrid(-2:2);
>> M = [X(:),Y(:)]
M =
    -2    -2
    -2    -1
    -2     0
    -2     1
    -2     2
    -1    -2
    -1    -1
    -1     0
    -1     1
    -1     2
     0    -2
     0    -1
     0     0
     0     1
     0     2
     1    -2
     1    -1
     1     0
     1     1
     1     2
     2    -2
     2    -1
     2     0
     2     1
     2     2

[Jan]

m and n can be arbitrary. Then ndgrid is needed.

[Kyle Young]

Meshgrid/ndgrid is definitely more simple, but how would you handle when m > 2?

Using the grid method, there needs to be an output stored for each level of 'm'.

I.e. for m = 2

[x,y] = ndgrid(-2:2);
T = [y(:),x(:)]

but for m = 4

[x,y,z,k] = ndgrid(-2:2);
T = [k(:),z(:),y(:),x(:)]

The number of outputs would change for every different 'm' value. Is this adaptable in Matlab?

Thanks

Answer 1

[Stephen23]

You can use comma-separated lists on the output of ndgrid:

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

m = 4;
C = cell(1,m);
[C{:}] = ndgrid(-2:2);
T = reshape(cat(m+1,C{:}),[],m)

T = 625×4

-2 -2 -2 -2 -1 -2 -2 -2 0 -2 -2 -2 1 -2 -2 -2 2 -2 -2 -2 -2 -1 -2 -2 -1 -1 -2 -2 0 -1 -2 -2 1 -1 -2 -2 2 -1 -2 -2 -2 0 -2 -2 -1 0 -2 -2 0 0 -2 -2 1 0 -2 -2 2 0 -2 -2

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[Kyle Young]

Great tutorial on comma separated lists. I didn't realize that was even an option for input/outputs. This will be very usefull forever more.

I'll need to read up on the cellfun(@(a)...) line, but this defintely works. Thanks, Stephen.

[Stephen23]

"Great tutorial on comma separated lists..."

Thank you, you can vote for it too, if you liked it :) Comma-separated lists are certainly very handy and well worth learning about.

"I'll need to read up on the cellfun(@(a)...) line..."

All that does lines does is convert the content of each cell (i.e. the array output from ndgrid) into a column vector. An explicit loop would likely be a tad faster, in case speed is of major concern.

https://www.mathworks.com/help/matlab/matlab_prog/anonymous-functions.html

Answer 2

[Walter Roberson]

ndgrid or meshgrid and reshape to column vectors and put the columns together.

Answer 3

[Jan]

With the fast C-Mex function https://www.mathworks.com/matlabcentral/fileexchange/26242-vchoosekro

R = VChooseKRO(-2:2, 2)

Or:

n   = 2;
m   = 2;
len = (2*n+1)^m;   % Not: (2*n-1)^m !
T   = zeros(len, m);
v   = repmat(-n, 1, m);
for k = 1:len
    T(k, :) = v;
    
    for im = m:-1:1
        if v(im) < n
            v(im) = v(im) + 1;
            break;
        end
        v(im) = -n;
    end
end

Or:

len = (2*n+1)^m;   % Not: (2*n-1)^m !
T  = zeros(len, m);
v  = (-n:n).';
nv = numel(v);
r1 = nv ^ (m - 1);
r2 = 1;
for k = 1:m
    T(:, k) = repmat(repelem(v, r1, 1), r2, 1);
    r1      = r1 / nv;
    r2      = r2 * nv;
end