what is wrong with this code?should i add instruction to declare X?

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lotus
lotus 2013-3-29
function X = sudoku(X)
% SUDOKU Solve Sudoku using recursive backtracking.
% sudoku(X), expects a 9-by-9 array X.
% Fill in all “singletons”.
% C is a cell array of candidate vectors for each cell.
% s is the first cell, if any, with one candidate.
% e is the first cell, if any, with no candidates.
[C,s,e] = candidates(X);
while ~isempty(s) && isempty(e)
X(s) = C{s};
[C,s,e] = candidates(X);
end
% Return for impossible puzzles.
if ~isempty(e)
return
end
% Recursive backtracking.
if any(X(:) == 0)
Y = X;
z = find(X(:) == 0,1); % The first unfilled cell.
for r = [C{z}] % Iterate over candidates.
X = Y;
X(z) = r; % Insert a tentative value.
X = sudoku(X); % Recursive call.
if all(X(:) > 0) % Found a solution.
return
end
end
end
% ------------------------------
function [C,s,e] = candidates(X)
C = cell(9,9);
tri = @(k) 3*ceil(k/3-1) + (1:3);
for j = 1:9
for i = 1:9
if X(i,j)==0
z = 1:9;
z(nonzeros(X(i,:))) = 0;
z(nonzeros(X(:,j))) = 0;
z(nonzeros(X(tri(i),tri(j)))) = 0;
C{i,j} = nonzeros(z)’;
end
end
end
L = cellfun(@length,C); % Number of candidates.
s = find(X==0 & L==1,1);
e = find(X==0 & L==0,1);
end % candidates
end % sudoku
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lotus
lotus 2013-3-29
when i run this code it said that Input argument "X" is undefined.
Error in ==> sudoku at 10
[C,s,e] = candidates(X);

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the cyclist
the cyclist 2013-3-29
It looks like you should be calling that function with the syntax
>> sudoku(X)
where X is a 9x9 array (which presumably represents the sudoku puzzle layout).
Is that what you are doing?
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Walter Roberson
Walter Roberson 2013-3-29
Assign a 9 x 9 matrix of initial values to a variable, such as Puzzle1. Then at the command line,
sodoku(Puzzle1)

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