/// <summary>
/// lower triangular part of matrix
/// </summary>
/// <typeparam name="T">inner type of matrix</typeparam>
/// <param name="A">original matrix, size [m x n]</param>
/// <returns>physical array of size [m x n], holding lower triangular part of A</returns>
/// <exception cref="ILNumerics.Exceptions.ILArgumentException"> if A has more than 2 dimensions.</exception>
public static ILArray <T> tril <T>(ILArray <T> A)
{
if (A.Dimensions.NumberOfDimensions > 2)
{
throw new ILArgumentException("tril: input argument must be matrix!");
}
return(A.copyLowerTriangle());
}