神秘约束中的变量占位符

Question

有什么方法可以在神秘约束中使用变量名吗？

即

equations = '''
abs(x0 - init_velocity) <= acceleration_constraint
abs(x1 - init_heading) <= turning_constraint
'''

以上导致此错误：

Traceback (most recent call last):

  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/IPython/core/interactiveshell.py", line 3418, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)

  File "<ipython-input-68-254fb3031193>", line 14, in <module>
    eqn = simplify(equations, all=True)

  File "<string>", line 120, in simplify

  File "<string>", line 93, in _simplify

  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/mystic/symbolic.py", line 381, in equals
    after, before = eval(after,{},locals_), eval(before,{},locals_)

  File "<string>", line unknown
    
    ^
SyntaxError: unexpected EOF while parsing

编辑：

下面使用的代码试图最小化当前局部点（x_0、y_0）和下一个局部点（x_1、y_1）之间的 l2 范数，同时遵循约束（物理加速度和转弯半径）。此距离相对于速度和航向最小化。

def formulate_objective(curr_x, curr_y, desired_x, desired_y):
    def objective(x):
        next_x = curr_x + x[0] * np.cos(np.radians(x[1]))
        next_y = curr_y + x[0] * np.sin(np.radians(x[1]))
        return np.linalg.norm(np.vstack([desired_x - next_x, desired_y - next_y]), ord=2)
    return objective

objective = formulate_objective(init_x, init_y, desired_x, desired_y)

equations = '''
abs(x0 - iv) <= ac
abs(x1 - ih) <= tc
'''
var_dict = dict(iv=init_velocity, ih=init_heading, 
                ac=acceleration_constraint, tc=turning_constraint)
eqn = simplify(equations, locals=var_dict)
cf = generate_constraint(generate_conditions(eqn, nvars=2), join=and_)

x0 = [init_velocity, init_heading]
fmin(objective, x0=x0, constraint=cf)

Answer 1

您可以使用所谓的 Python f-Strings:

https://realpython.com/python-f-strings/

示例：

k = 'x0'
i = 'init_velocity'
a = 'acceleration_constraint'
b = 'turning_constraint'
equations = f'''
abs({k} - {i}) <= {a}
abs({k} - {i}) <= {b}
'''
print(equations)

给我这个输出：

abs(x0 - init_velocity) <= acceleration_constraint
abs(x0 - init_velocity) <= turning_constraint

Answer 2

您应该能够使用 locals 关键字来替换不是优化变量名称的名称。

>>> import mystic.symbolic as ms
>>> equations = '''
... x0 + x1 = A
... x1 * x0 = B
... '''
>>> 
>>> eqn = ms.simplify(equations, locals=dict(A=7,B=12))
>>> print(eqn)
x0 = 7 - x1
x0 != 0
x1 = 12/x0
>>>

神秘约束中的变量占位符

Variable placeholder in mystic constraints

python

optimization

constraints

mystic