from cvxopt import matrix, spmatrix

def append_col(A,b):
    """
    Append the column ``b`` to the right side of the matrix ``A``.
    """
    return matrix([A.trans(),b.trans()]).trans()

def append_cols(cols):
    """
    Append a bunch of columns together, left to right.
    """
    if len(cols) == 0:
        return cols

    result = cols[0]
    del(cols[0])
    for column in cols:
        result = append_col(result, column)

    return result


def append_row(A,b):
    """
    Append the row ``b`` to the bottom of the matrix ``A``.
    """
    return matrix([A,b])

def identity(n):
    """
    Return the ``n``-by-``n`` identity matrix.
    """
    return spmatrix(1,range(n),range(n))