实例化一个std ::升压的矢量:: multi_array ..为CPP大师融化大脑？

Question

我觉得我与实例化对象混淆了..很好......不是正确的对象，因为世代odicetagcode语句进行编译错误。我的背景是在Python和Java中，我陷入了C ++的方式，它的创建不是类的对象。

我正在从c＃和机器学习翻译算法，它使用多维数组数组。

c＃代码：

public double Learn(int[][] observations, int symbols, int states, ...

    // ...

    double[][, ,] epsilon = new double[N][, ,]; // also referred as ksi or psi
    double[][,] gamma = new double[N][,];

    for (int i = 0; i < N; i++)
    {
        int T = observations[i].Length;
        epsilon[i] = new double[T, States, States];
        gamma[i] = new double[T, States];
    }

.

我决定使用多维数组的Boost库，我有：

typedef boost::multi_array<double, 2> matrix2D;
typedef boost::multi_array<double, 3> matrix3D;

vector<matrix3D> epsilon;
vector<matrix2D> gamma;

cout << "HMM::learn >> before" << endl;
for (int i = 0; i < N; i++)
{
    int T = observations[i].size();
    epsilon[i] = matrix3D(boost::extents[T][states][symbols]);
    gamma[i] = matrix2D(boost::extents[T][states]);
}

.

，我得到这个运行时错误：

hmm ::学习>>之前 std :: bad_alloc'什么（）：std :: bad_alloc

Answer 1

The vectors have no space allocated (well it may be reserved already but you can't reference it with the array indexers). Change the lines:

epsilon[i] = matrix3D(boost::extents[T][states][symbols]);
gamma[i] = matrix2D(boost::extents[T][states]);

To:

epsilon.push_back(matrix3D(boost::extents[T][states][symbols]);
gamma.push_back(matrix2D(boost::extents[T][states]);

that should solve it. In your case since you know the array size you should reserve that much space in the vectors so that it reduces the reallocations needed:

epsilon.reserve(N);
gamma.reserve(N);