private DoubleMatrix getDiffMatrix(int[] size, int k, int indices)
{
int dim = size.Length;
DoubleMatrix d = getDiffMatrix(size[indices], k);
int preProduct = 1;
int postProduct = 1;
for (int j = indices + 1; j < dim; j++)
{
preProduct *= size[j];
}
for (int j = 0; j < indices; j++)
{
postProduct *= size[j];
}
DoubleMatrix temp = d;
if (preProduct != 1)
{
temp = (DoubleMatrix)_algebra.kroneckerProduct(DoubleMatrix.identity(preProduct), temp);
}
if (postProduct != 1)
{
temp = (DoubleMatrix)_algebra.kroneckerProduct(temp, DoubleMatrix.identity(postProduct));
}
return(temp);
}
/// <summary>
/// Assume a tensor has been flattened to a vector as {A_{0,0}, A_{0,1},...._A_{0,m}, A_{1,0}, A_{1,1},...._A_{1,m},...,A_{n,0}, A_{n,1},...._A_{n,m}}
/// (see <seealso cref="#flattenMatrix"/>) that is, the <b>last</b> index changes most rapidly.
/// Given a matrix, M, that acts on the elements of one index only, i.e.
/// $$y_{i, i_1, i_2, \dots,i_{k-1}, i_{k+1},\dots, i_n} = \sum_{i_k=0}^{N_k-1} M_{i,i_k} x_{i_1, i_2, \dots,i_k,\dots, i_n} $$
/// form the larger matrix that acts on the flattened vector. </summary>
/// <param name="numElements"> The number of elements in each index. In the example above, this would be {n,m} </param>
/// <param name="m"> the matrix M </param>
/// <param name="index"> Which index does the matrix act on </param>
/// <returns> A (larger) matrix which acts on the flattened vector </returns>
public static DoubleMatrix getMatrixForFlattened(int[] numElements, DoubleMatrix m, int index)
{
ArgChecker.notEmpty(numElements, "numElements");
int dim = numElements.Length;
ArgChecker.notNull(m, "m");
ArgChecker.isTrue(index >= 0 && index < dim, "indices outside range");
ArgChecker.isTrue(m.columnCount() == numElements[index], "columns in m ({}) do not match numElements for index ({})", m.columnCount(), numElements[index]);
int postProduct = 1;
int preProduct = 1;
for (int j = index + 1; j < dim; j++)
{
preProduct *= numElements[j];
}
for (int j = 0; j < index; j++)
{
postProduct *= numElements[j];
}
DoubleMatrix temp = m;
if (preProduct != 1)
{
temp = (DoubleMatrix)MA.kroneckerProduct(temp, DoubleMatrix.identity(preProduct));
}
if (postProduct != 1)
{
temp = (DoubleMatrix)MA.kroneckerProduct(DoubleMatrix.identity(postProduct), temp);
}
return(temp);
}