Question

我在OpenMDAO（http://openmdao.readthedocs.io/en/1.7.3/usr-guide/tutorials/sellar.html）的doc页面上发现了一些关于鞍座问题的MDA的奇怪内容

如果我提取代码并且仅运行MDA（在学科中添加计数器），我观察到调用的数量是不同学科之间的差异（d1学科的d2的两倍），这是不期望的。有人有答案吗？

以下是结果

Coupling vars：25.588303,12.058488 学科1和2电话的数量（10,5）

这是代码

# For printing, use this import if you are running Python 2.x from __future__ import print_function


import numpy as np

from openmdao.api import Component from openmdao.api import ExecComp, IndepVarComp, Group, NLGaussSeidel, \
                         ScipyGMRES

class SellarDis1(Component):
    """Component containing Discipline 1."""

    def __init__(self):
        super(SellarDis1, self).__init__()

        # Global Design Variable
        self.add_param('z', val=np.zeros(2))

        # Local Design Variable
        self.add_param('x', val=0.)

        # Coupling parameter
        self.add_param('y2', val=1.0)

        # Coupling output
        self.add_output('y1', val=1.0)
        self.execution_count = 0

    def solve_nonlinear(self, params, unknowns, resids):
        """Evaluates the equation
        y1 = z1**2 + z2 + x1 - 0.2*y2"""

        z1 = params['z'][0]
        z2 = params['z'][1]
        x1 = params['x']
        y2 = params['y2']

        unknowns['y1'] = z1**2 + z2 + x1 - 0.2*y2
        self.execution_count += 1
    def linearize(self, params, unknowns, resids):
        """ Jacobian for Sellar discipline 1."""
        J = {}

        J['y1','y2'] = -0.2
        J['y1','z'] = np.array([[2*params['z'][0], 1.0]])
        J['y1','x'] = 1.0

        return J


class SellarDis2(Component):
    """Component containing Discipline 2."""

    def __init__(self):
        super(SellarDis2, self).__init__()

        # Global Design Variable
        self.add_param('z', val=np.zeros(2))

        # Coupling parameter
        self.add_param('y1', val=1.0)

        # Coupling output
        self.add_output('y2', val=1.0)
        self.execution_count = 0
    def solve_nonlinear(self, params, unknowns, resids):
        """Evaluates the equation
        y2 = y1**(.5) + z1 + z2"""

        z1 = params['z'][0]
        z2 = params['z'][1]
        y1 = params['y1']

        # Note: this may cause some issues. However, y1 is constrained to be
        # above 3.16, so lets just let it converge, and the optimizer will
        # throw it out
        y1 = abs(y1)

        unknowns['y2'] = y1**.5 + z1 + z2
        self.execution_count += 1
    def linearize(self, params, unknowns, resids):
        """ Jacobian for Sellar discipline 2."""
        J = {}

        J['y2', 'y1'] = .5*params['y1']**-.5

        #Extra set of brackets below ensure we have a 2D array instead of a 1D array
        # for the Jacobian;  Note that Jacobian is 2D (num outputs x num inputs).
        J['y2', 'z'] = np.array([[1.0, 1.0]])

        return J



class SellarDerivatives(Group):
    """ Group containing the Sellar MDA. This version uses the disciplines
    with derivatives."""

    def __init__(self):
        super(SellarDerivatives, self).__init__()

        self.add('px', IndepVarComp('x', 1.0), promotes=['x'])
        self.add('pz', IndepVarComp('z', np.array([5.0, 2.0])), promotes=['z'])

        self.add('d1', SellarDis1(), promotes=['z', 'x', 'y1', 'y2'])
        self.add('d2', SellarDis2(), promotes=['z', 'y1', 'y2'])

        self.add('obj_cmp', ExecComp('obj = x**2 + z[1] + y1 + exp(-y2)',
                                     z=np.array([0.0, 0.0]), x=0.0, y1=0.0, y2=0.0),
                 promotes=['obj', 'z', 'x', 'y1', 'y2'])

        self.add('con_cmp1', ExecComp('con1 = 3.16 - y1'), promotes=['y1', 'con1'])
        self.add('con_cmp2', ExecComp('con2 = y2 - 24.0'), promotes=['con2', 'y2'])

        self.nl_solver = NLGaussSeidel()
        self.nl_solver.options['atol'] = 1.0e-12

        self.ln_solver = ScipyGMRES()
         from openmdao.api import Problem, ScipyOptimizer

top = Problem() top.root = SellarDerivatives()

#top.driver = ScipyOptimizer()
#top.driver.options['optimizer'] = 'SLSQP'
#top.driver.options['tol'] = 1.0e-8
#
#top.driver.add_desvar('z', lower=np.array([-10.0, 0.0]),
#                     upper=np.array([10.0, 10.0]))
#top.driver.add_desvar('x', lower=0.0, upper=10.0)
#
#top.driver.add_objective('obj')
#top.driver.add_constraint('con1', upper=0.0)
#top.driver.add_constraint('con2', upper=0.0)

top.setup()

# Setting initial values for design variables top['x'] = 1.0 top['z'] = np.array([5.0, 2.0])

top.run()

print("\n")

print("Coupling vars: %f, %f" % (top['y1'], top['y2']))


count1 = top.root.d1.execution_count 
count2 = top.root.d2.execution_count 
print("Number of discipline 1 and 2 calls (%i,%i)"% (count1,count2))

Answer 1

这是一个很好的观察。只要你有一个循环，“head”组件就会再次运行。原因如下：

如果您的模型包含隐式状态的组件，则单个执行如下所示：

致电solve_nonlinear执行组件
致电apply_nonlinear计算残差。

我们在此模型中没有任何具有隐式状态的组件，但是我们通过循环间接创建了对组件的需求。我们的执行如下：

致电solve_nonlinear以执行所有组件。
调用apply_nonlinear（缓存未知数，调用solve_nolinear，并将未知数的差异保存在“head”组件上，以生成我们可以收敛的残差。

这里，head组件只是第一个基于它执行的组件，但是它决定了循环运行的顺序。通过构建一个包含2个以上组件的循环，可以验证只有单个组件可以获得额外的运行

Openmdao V1.7 Sellar MDF

1 个答案: