MATLAB: Error “too many output argument” in function

matlab function

I just have try some of applied physics here and try to run the code in Matlab R2019b. after some step, about separate the code become function. it became
Error using initSpins1
Too many output arguments.
Error in Metro2 (line 9)
spin  = initSpins1(numSpinsPerDim, probSpinUp);
I also write the program right below,
numSpinsPerDim = 2^3;
probSpinUp = 0.5;
numTemps = 2^9; 
kTc = 2*J / log(1+sqrt(2)); % Curie temperature
kT = linspace(0, 2*kTc, numTemps);
% Preallocate to store results
Emean = zeros(size(kT));
Mmean = zeros(size(kT));
% Replace 'for' with 'parfor' to run in parallel with Parallel Computing Toolbox.
parfor tempIndex = 1:numTemps
    spin = initSpins1(numSpinsPerDim,probSpinUp);
    spin = Metropolisalgo1(spin, kT(tempIndex), J);
    Emean(tempIndex) = energyIsingalgo1(spin, J);
    Mmean(tempIndex) = magnetizationIsingalgo1(spin);
end
and each of function like,
function initSpins1(numSpinsPerDim, probSpinUp);
    spin = sign(probSpinUp - rand(numSpinsPerDim, numSpinsPerDim));
end
function metropolisalgo1(spin, kT, J);% Metropolis algorithm
    numIters = 2^7 * numel(spin);
    for iter = 1 : numIters
        % Pick a random spin
        linearIndex = randi(numel(spin));
        [row, col]  = ind2sub(size(spin), linearIndex);
        % Find its nearest neighbors
        above = mod(row - 1 - 1, size(spin,1)) + 1;
        below = mod(row + 1 - 1, size(spin,1)) + 1;
        left  = mod(col - 1 - 1, size(spin,2)) + 1;
        right = mod(col + 1 - 1, size(spin,2)) + 1;
        neighbors = [      spin(above,col);
            spin(row,left);                spin(row,right);
                           spin(below,col)];
        % Calculate energy change if this spin is flipped
        dE = 2 * J * spin(row, col) * sum(neighbors);
        % Boltzmann probability of flipping
        prob = exp(-dE / kT);
        % Spin flip condition
        if dE <= 0 || rand() <= prob
            spin(row, col) = - spin(row, col);
        end
    end
end
function energyIsingalgo1(spin, J);
    % The mean energy
    sumOfNeighbors = ...
          circshift(spin, [ 0  1]) ...
        + circshift(spin, [ 0 -1]) ...
        + circshift(spin, [ 1  0]) ...
        + circshift(spin, [-1  0]);
    Em = - J * spin .* sumOfNeighbors;
    E  = 0.5 * sum(Em(:));
    Emean = E / numel(spin);
end
function magnetizationIsingalgo1(spin);
    Mmean = mean(spin(:));
end
How should I do to fix the error? thanks

Best Answer

"How should I do to fix the error?"
If you want a function to return an output then the it must be defined in the function declaration, e.g.:
function spin = initSpins1(numSpinsPerDim, probSpinUp)
%        ^^^^^^^ you need this!
This is explained in the function documentation (which also shows how to return multiple outputs):
https://www.mathworks.com/help/matlab/ref/function.html
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