/// <summary>
/// Return a 2-D array with ones on the diagonal and zeros elsewhere.
/// </summary>
/// <param name="N">Number of rows in the output.</param>
/// <param name="M">Number of columns in the output. If None, defaults to N.</param>
/// <param name="k">Index of the diagonal: 0 (the default) refers to the main diagonal, a positive value refers to an upper diagonal, and a negative value to a lower diagonal.</param>
/// <param name="dtype">Data-type of the returned array.</param>
/// <returns>An array where all elements are equal to zero, except for the k-th diagonal, whose values are equal to one.</returns>
/// <remarks>https://docs.scipy.org/doc/numpy/reference/generated/numpy.eye.html</remarks>
public static NDArray eye(int N, int?M = null, int k = 0, Type dtype = null)
{
if (!M.HasValue)
{
M = N;
}
var m = np.zeros(Shape.Matrix(N, M.Value), dtype ?? typeof(double));
if (k >= M)
{
return(m);
}
int i;
if (k >= 0)
{
i = k;
}
else
{
i = (-k) * M.Value;
}
var flat = m.flat;
var one = dtype != null?Converts.ChangeType(1d, dtype.GetTypeCode()) : 1d;
int skips = k < 0 ? Math.Abs(k) - 1 : 0;
for (int j = k; j < flat.size; j += N + 1)
{
if (j < 0 || skips-- > 0)
{
continue;
}
flat.SetAtIndex(one, j);
}
return(m);
}
public static NDArray array <T>(T[][] data)
{
var array = data.SelectMany(inner => inner).ToArray(); //todo! not use selectmany.
return(new NDArray(array, Shape.Matrix(data.Length, data[0].Length)));
}
