在Sympy中隐式linsolve()，然后使用lambdify

Question

我想问的是，在一个涉及求解的表达式中，是否有可能将np.linalg.solve()从lambdify中提取出来？

例如，让

from sympy import MatrixSymbol, linsolve, lambdify

A = MatrixSymbol('A', 3, 3)
b = MatrixSymbol('b', 3, 1)

func = lambdify((A, b), linsolve((A, b)), modules="numpy")

是否可以生成func(A, b) = np.linalg.solve(A, b)

以上代码肯定不起作用。它将首先在linsolve((A, b))失败。

我的尝试是将linsolve((A, b))标记为一个隐式表达式，以便lambdify能够识别它，从而将它与np.linalg.solve连接起来。但我不知道sympy是否支持这一点。

Answer 1

您可以使用函数sympy.codegen.matrix_nodes.MatrixSolve而不是sympy.linsolve。

from sympy import MatrixSymbol, lambdify
from sympy.codegen.matrix_nodes import MatrixSolve

A = MatrixSymbol('A', 3, 3)
b = MatrixSymbol('b', 3, 1)


func = lambdify((A, b), MatrixSolve(A, b), modules="numpy")

Answer 2

使用MatrixSolve，lambdify执行一个简单的词法替换：

In [87]: MatrixSolve(A,b)
Out[87]: MatrixSolve(MatrixSymbol(Str('A'), Integer(3), Integer(3)), vector=MatrixSymbol(Str('b'), Integer(3), Integer(1)))

In [88]: func = lambdify((A, b), MatrixSolve(A, b), modules="numpy")

In [89]: func
Out[89]: <function _lambdifygenerated(A, b)>

In [90]: func?
Signature: func(A, b)
Docstring:
Created with lambdify. Signature:

func(A, b)

Expression:

MatrixSolve(A, vector=b)

Source code:

def _lambdifygenerated(A, b):
    return (solve(A, b))

或者使用print(func.__doc__)显示该文档(如果不是在ipython/isympy中)。

你最初的问题是使用sympy.linsolve

In [81]: linsolve((A,b))
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-81-9ddeeeb0f242> in <module>
----> 1 linsolve((A,b))

/usr/local/lib/python3.8/dist-packages/sympy/solvers/solveset.py in linsolve(system, *symbols)
   2630         if not isinstance(system[0], MatrixBase):
   2631             if sym_gen or not symbols:
-> 2632                 raise ValueError(filldedent('''
   2633                     When passing a system of equations, the explicit
   2634                     symbols for which a solution is being sought must

ValueError: 
When passing a system of equations, the explicit symbols for which a
solution is being sought must be given as a sequence, too.