Python sympy 模块，diag() 实例源码

def construct_explicit_matrix(name, n, m, symmetric=False, diagonal=0,
                              dynamic=False, **kwass):
    """
    construct a matrix of symbolic elements

    Parameters
    ----------
    name : string
        Base name for variables; each variable is name_ij, which
        admitedly only works clearly for n,m < 10
    n : int
        Number of rows
    m : int
        Number of columns
    symmetric : bool, optional
        Use to enforce a symmetric matrix (repeat symbols above/below diagonal)
    diagonal : bool, optional
        Zeros out off diagonals. Takes precedence over symmetry.
    dynamic : bool, optional
        Whether to use sympy.physics.mechanics dynamicsymbol. If False, use
        sp.symbols
    kwargs : dict
        remaining kwargs passed to symbol function

    Returns
    -------
    matrix : sympy Matrix
        The Matrix containing explicit symbolic elements
    """
    if dynamic:
        symbol_func = dynamicsymbols
    else:
        symbol_func = sp.symbols

    if n != m and (diagonal or symmetric):
        raise ValueError("Cannot make symmetric or diagonal if n != m")

    if diagonal:
        return sp.diag(
            *[symbol_func(
                name+'_{}{}'.format(i+1, i+1), **kwass) for i in range(m)])
    else:
        matrix = sp.Matrix([
            [symbol_func(name+'_{}{}'.format(j+1, i+1), **kwass)
             for i in range(m)] for j in range(n)
        ])

        if symmetric:
            for i in range(1, m):
                for j in range(i):
                    matrix[i, j] = matrix[j, i]
        return matrix