Converting binary like table but using decimal values

Question

Kyle Young 2019-5-6

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编辑： Stephen23 2019-5-7

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!

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Jan 2019-5-7

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

Kyle Young 2019-5-7

在 MATLAB Online 中打开

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

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Answer 1

Stephen23 2019-5-7

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编辑：Stephen23 2019-5-7

在 MATLAB Online 中打开

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);
>> C = cellfun(@(a)a(:),C,'uni',0);
>> T = [C{end:-1:1}]
ans =
  -2  -2  -2  -2
  -2  -2  -2  -1
  -2  -2  -2   0
  -2  -2  -2   1
  -2  -2  -2   2
  -2  -2  -1  -2
  -2  -2  -1  -1
  -2  -2  -1   0
  -2  -2  -1   1
  -2  -2  -1   2
  -2  -2   0  -2
  -2  -2   0  -1
  -2  -2   0   0
  -2  -2   0   1
  -2  -2   0   2
... lots of lines here
   2   2   1   1
   2   2   1   2
   2   2   2  -2
   2   2   2  -1
   2   2   2   0
   2   2   2   1
   2   2   2   2

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Kyle Young 2019-5-7

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 2019-5-7

编辑：Stephen23 2019-5-7

"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

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Answer 2

Walter Roberson 2019-5-6

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

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Answer 3

Jan 2019-5-7

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https://ww2.mathworks.cn/matlabcentral/answers/460547-converting-binary-like-table-but-using-decimal-values#answer_373925

编辑：Jan 2019-5-7

在 MATLAB Online 中打开

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