Octave error: no default value for argument 1 while calling function

Question

我需要按列为每个值查找 normalized 值。所以我有这样的功能：

function [X_norm, mu, sigma] = featureNormalize(X)

X_norm = X;
mu = zeros(1, size(X, 2));
sigma = zeros(1, size(X, 2));

for x = 1:size(X, 1)
    mu(1,x) = mean(:, x)
    sigma(1,x) = std(:, x)
    for y = 1:size(X, 2)  
        X_norm(x,y) = (X(x,y) - mu)/sigma
    end  
end    

end

我正在尝试以这种方式调用此函数：

>> X = [23 32 2 ; 23 23 1];
>> featureNormalize(X)

结果我得到这样的错误：调用函数时参数 1 没有默认值。我不明白这里有什么问题，有什么建议吗？

Answer 1

我认为您使用 mean() 和 std() 函数的方式存在问题，下标赋值也可能是一个问题。

我不确定，但请尝试使用下面这些代码作为您的函数定义：

1.基于行的规范化：

function [X_norm, mu, sigma] = featureNormalize(X)

X_norm = zeros(size(X));
mu     = zeros(1, size(X, 1));
sigma  = zeros(1, size(X, 1));

for x = 1:size(X, 1)
    mu(x)    = mean( X(x, :) );
    sigma(x) = std( X(x, :) );

    for y = 1 : size(X, 2)  
        X_norm(x, y) = ( X(x, y) - mu(x) ) / sigma(x);
    end  
end     
end

2。基于列的归一化：

function [X_norm, mu, sigma] = featureNormalize(X)

X_norm = zeros(size(X));
mu     = zeros(1, size(X, 2));
sigma  = zeros(1, size(X, 2));

for y = 1:size(X, 2)
    mu(y)    = mean( X(:, y) );
    sigma(y) = std( X(:, y) );

    for x = 1 : size(X, 1)  
        X_norm(x, y) = ( X(x, y) - mu(y) ) / sigma(y);
    end  
end     
end

Answer 2

如果您要针对每个列的 mean 和 sigma 值计算每个元素的归一化值，我认为您需要由于您使用的是 mean 和 sigma 值的数组，因此您的问题代码并没有真正反映出一些变化。所以，我认为你需要做这样的事情 -

%// Initialize array for final normalized values
X_norm = zeros(size(X));
for x = 1:size(X, 2)

    %// Store mean and standard deviation values for each column
    mu = mean(X(:, x))
    sigma = std(X(:, x))

    %// Use an innermost loop to calculate the normalized values 
    %// for all the elements in each column. 
    %// Thus, for all these elements, you need to use the same mean
    %// and standard deviation calculated in the previous step
    for y = 1:size(X, 1)  
        X_norm(y,x) = (X(y,x) - mu)/sigma
    end  
end

你可以很容易地向量化上面的代码 bsxfun -

X_norm = bsxfun(@rdivide, bsxfun(@minus, X, mean(X,1)),std(X,[],1))

Octave error: no default value for argument 1 while calling function

Octave error: no default value for argument 1 while calling function

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