def multiply(a, col):
    """Multiply a matrix by one column."""
    a = a.reshape(4, 4, 4)
    col = col.reshape(4, 8)
    return fcat(
        rowxcol(a[0], col),
        rowxcol(a[1], col),
        rowxcol(a[2], col),
        rowxcol(a[3], col),
    )
Multiply a matrix by one column.