##############################################################################
# Institute for the Design of Advanced Energy Systems Process Systems
# Engineering Framework (IDAES PSE Framework) Copyright (c) 2018-2020, by the
# software owners: The Regents of the University of California, through
# Lawrence Berkeley National Laboratory, National Technology & Engineering
# Solutions of Sandia, LLC, Carnegie Mellon University, West Virginia
# University Research Corporation, et al. All rights reserved.
#
# Please see the files COPYRIGHT.txt and LICENSE.txt for full copyright and
# license information, respectively. Both files are also available online
# at the URL "https://github.com/IDAES/idaes-pse".
##############################################################################
"""
This module contains utilities to provide variable and expression scaling
factors by providing an expression to calculate them via a suffix.
The main purpose of this code is to use the calculate_scaling_factors function
to calculate scaling factors to be used with the Pyomo scaling transformation or
with solvers. A user can provide a scaling_expression suffix to calculate scale
factors from existing variable scaling factors. This allows scaling factors from
a small set of fundamental variables to be propagated to the rest of the model.
The scaling_expression suffix contains Pyomo expressions with model variables.
The expressions can be evaluated with variable scaling factors in place of
variables to calculate additional scaling factors.
"""
__author__ = "John Eslick, Tim Bartholomew"
import pyomo.environ as pyo
from pyomo.core.expr import current as EXPR
from pyomo.core.expr.visitor import identify_variables
from pyomo.network import Arc
from pyomo.contrib.pynumero.interfaces.pyomo_nlp import PyomoNLP
from pyomo.common.modeling import unique_component_name
from pyomo.core.base.constraint import _ConstraintData
from pyomo.common.collections import ComponentMap
from pyomo.util.calc_var_value import calculate_variable_from_constraint
from idaes.core.util.exceptions import ConfigurationError
import idaes.logger as idaeslog
__author__ = "John Eslick, Tim Bartholomew, Robert Parker"
_log = idaeslog.getLogger(__name__)
def __none_mult(x, y):
"""PRIVATE FUNCTION, If x or y is None return None, else return x * y"""
if x is not None and y is not None:
return x * y
return None
def scale_arc_constraints(blk):
"""Find Arc constraints in a block and its subblocks. Then scale them based
on the minimum scaling factor of the variables in the constraint.
Args:
blk: Block in which to look for Arc constraints to scale.
Returns:
None
"""
for arc in blk.component_data_objects(Arc, descend_into=True):
arc_block = arc.expanded_block
if arc_block is None: # arc not expanded or port empty?
_log.warning(
f"{arc} has no constraints. Has the Arc expansion transform "
"been appied?")
continue
for c in arc_block.component_data_objects(pyo.Constraint, descend_into=True):
sf = min_scaling_factor(identify_variables(c.body))
constraint_scaling_transform(c, sf)
[docs]def map_scaling_factor(iter, default=1, warning=False, func=min):
"""Map get_scaling_factor to an iterable of Pyomo components, and call func
on the result. This could be use, for example, to get the minimum or
maximum scaling factor of a set of components.
Args:
iter: Iterable yeilding Pyomo componentes
default: The default value used when a scaling factor is missing. The
default is default=1.
warning: Log a warning for missing scaling factors
func: The function to call on the resulting iterable of scaling factors.
The default is min().
Returns:
The result of func on the set of scaling factors
"""
return func(
map(
lambda x: get_scaling_factor(x, default=default, warning=warning),
iter
)
)
[docs]def min_scaling_factor(iter, default=1, warning=True):
"""Map get_scaling_factor to an iterable of Pyomo components, and get the
minimum caling factor.
Args:
iter: Iterable yeilding Pyomo componentes
default: The default value used when a scaling factor is missing. If
None, this will raise an exception when scaling factors are missing.
The default is default=1.
warning: Log a warning for missing scaling factors
Returns:
Minimum scaling factor of the components in iter
"""
return map_scaling_factor(iter, default=default, warning=warning, func=min)
[docs]def propagate_indexed_component_scaling_factors(
blk,
typ=(pyo.Var, pyo.Constraint, pyo.Expression),
overwrite=False,
descend_into=True):
"""Use the parent component scaling factor to set all component data object
scaling factors.
Args:
blk: The block on which to search for components
typ: Component type(s) (default=(Var, Constraint, Expression, Param))
overwrite: if a data object already has a scaling factor should it be
overwrittten (default=False)
descend_into: descend into child blocks (default=True)
"""
for c in blk.component_objects(typ, descend_into=descend_into):
if get_scaling_factor(c) is not None and c.is_indexed():
for cdat in c.values():
if overwrite or get_scaling_factor(cdat) is None:
set_scaling_factor(cdat, get_scaling_factor(c))
def calculate_scaling_factors(blk):
"""Look for calculate_scaling_factors methods and run them. This uses a
recursive function to execute the subblock calculate_scaling_factors
methods first.
"""
def cs(blk2):
""" Recursive function for to do subblocks first"""
for b in blk2.component_data_objects(pyo.Block, descend_into=False):
cs(b)
if hasattr(blk2, "calculate_scaling_factors"):
blk2.calculate_scaling_factors()
# Call recursive function to run calculate_scaling_factors on blocks from
# the bottom up.
cs(blk)
# If a scale factor is set for an indexed component, propagate it to the
# component data if a scale factor hasn't already been explicitly set
propagate_indexed_component_scaling_factors(blk)
# Use the variable scaling factors to scale the arc constraints.
scale_arc_constraints(blk)
[docs]def set_scaling_factor(c, v, data_objects=True):
"""Set a scaling factor for a model component. This function creates the
scaling_factor suffix if needed.
Args:
c: component to supply scaling factor for
v: scaling factor
Returns:
None
"""
if isinstance(c, (float, int)):
# property packages can return 0 for material balance terms on components
# doesn't exist. This handles the case where you get a constant 0 and
# need it's scale factor to scale the mass balance.
return 1
try:
suf = c.parent_block().scaling_factor
except AttributeError:
c.parent_block().scaling_factor = pyo.Suffix(direction=pyo.Suffix.EXPORT)
suf = c.parent_block().scaling_factor
suf[c] = v
if data_objects and c.is_indexed():
for cdat in c.values():
suf[cdat] = v
[docs]def get_scaling_factor(c, default=None, warning=False, exception=False):
"""Get a component scale factor.
Args:
c: component
default: value to return if no scale factor exists (default=None)
"""
try:
sf = c.parent_block().scaling_factor[c]
except (AttributeError, KeyError):
if warning:
_log.warning(f"Accessing missing scaling factor for {c}")
if exception and default is None:
_log.error(f"Accessing missing scaling factor for {c}")
raise
sf = default
return sf
[docs]def unset_scaling_factor(c, data_objects=True):
"""Delete a component scaling factor.
Args:
c: component
Returns:
None
"""
try:
del c.parent_block().scaling_factor[c]
except (AttributeError, KeyError):
pass # no scaling factor suffix, is fine
try:
if data_objects and c.is_indexed():
for cdat in c.values():
del cdat.parent_block().scaling_factor[cdat]
except (AttributeError, KeyError):
pass # no scaling factor suffix, is fine
def __set_constraint_transform_applied_scaling_factor(c, v):
"""PRIVATE FUNCTION Set the scaling factor used to transform a constraint.
This is used to keep track of scaling tranformations that have been applied
to constraints.
Args:
c: component to supply scaling factor for
v: scaling factor
Returns:
None
"""
try:
c.parent_block().constaint_transformed_scaling_factor[c] = v
except AttributeError:
c.parent_block().constaint_transformed_scaling_factor = pyo.Suffix(
direction=pyo.Suffix.LOCAL)
c.parent_block().constaint_transformed_scaling_factor[c] = v
def __unset_constraint_transform_applied_scaling_factor(c):
"""PRIVATE FUNCTION: Delete the recorded scale factor that has been used
to transform constraint c. This is used when undoing a constraint
transformation.
"""
try:
del c.parent_block().constaint_transformed_scaling_factor[c]
except AttributeError:
pass # no scaling factor suffix, is fine
except KeyError:
pass # no scaling factor is fine
[docs]def unscaled_variables_generator(blk, descend_into=True, include_fixed=False):
"""Generator for unscaled variables
Args:
block
Yields:
variables with no scale factor
"""
for v in blk.component_data_objects(pyo.Var, descend_into=descend_into):
if v.fixed and not include_fixed:
continue
if get_scaling_factor(v) is None:
yield v
[docs]def unscaled_constraints_generator(blk, descend_into=True):
"""Generator for unscaled constraints
Args:
block
Yields:
constraints with no scale factor
"""
for c in blk.component_data_objects(
pyo.Constraint, active=True, descend_into=descend_into):
if get_scaling_factor(c) is None and \
get_constraint_transform_applied_scaling_factor(c) is None:
yield c
[docs]def badly_scaled_var_generator(
blk, large=1e4, small=1e-3, zero=1e-10, descend_into=True, include_fixed=False):
"""This provides a rough check for variables with poor scaling based on
their current scale factors and values. For each potentially poorly scaled
variable it returns the var and its current scaled value.
Args:
blk: pyomo block
large: Magnitude that is considered to be too large
small: Magnitude that is considered to be too small
zero: Magnitude that is considered to be zero, variables with a value of
zero are okay, and not reported.
Yields:
variable data object, current absolute value of scaled value
"""
for v in blk.component_data_objects(pyo.Var, descend_into=descend_into):
if v.fixed and not include_fixed:
continue
val = pyo.value(v, exception=False)
if val is None:
continue
sf = get_scaling_factor(v, default=1)
sv = abs(val * sf) # scaled value
if sv > large:
yield v, sv
elif sv < zero:
continue
elif sv < small:
yield v, sv
[docs]def constraint_autoscale_large_jac(
m,
ignore_constraint_scaling=False,
ignore_variable_scaling=False,
max_grad=100,
min_scale=1e-6,
no_scale = False
):
"""Automatically scale constraints based on the Jacobian. This function
immitates Ipopt's default constraint scaling. This scales constraints down
to avoid extremely large values in the Jacobian
Args:
m: model to scale
ignore_constraint_scaling: ignore existing constraint scaling
ignore_variable_scaling: ignore existing variable scaling
max_grad: maximum value in Jacobian after scaling, subject to minimum
scaling factor restriction.
min_scale: minimum scaling factor allowed, keeps constraints from being
scaled too much.
no_scale: just calculate the Jacobian and scaled Jacobian, don't scale
anything
"""
# Pynumero requires an objective, but I don't, so let's see if we have one
n_obj = 0
for c in m.component_data_objects(pyo.Objective, active=True):
n_obj += 1
# Add an objective if there isn't one
if n_obj == 0:
dummy_objective_name = unique_component_name(m, "objective")
setattr(m, dummy_objective_name, pyo.Objective(expr=0))
# Create NLP and calculate the objective
nlp = PyomoNLP(m)
jac = nlp.evaluate_jacobian().tocsr()
# Get lists of varibles and constraints to translate Jacobian indexes
clist = nlp.get_pyomo_constraints()
vlist = nlp.get_pyomo_variables()
# Create a scaled Jacobian to account for variable scaling, for now ignore
# constraint scaling
jac_scaled = jac.copy()
for i in range(len(clist)):
for j in jac_scaled[i].indices:
v = vlist[j]
if ignore_variable_scaling:
sv = 1
else:
sv = get_scaling_factor(v, default=1)
jac_scaled[i,j] = jac_scaled[i,j]/sv
# calculate constraint scale factors
for i in range(len(clist)):
c = clist[i]
sc = get_scaling_factor(c, default=1)
if not no_scale:
if (ignore_constraint_scaling or get_scaling_factor(c) is None):
row = jac_scaled[i]
for d in row.indices:
row[0,d] = abs(row[0,d])
mg = row.max()
if mg > max_grad:
sc = max(min_scale, max_grad/mg)
set_scaling_factor(c, sc)
for j in jac_scaled[i].indices:
# update the scaled jacobian
jac_scaled[i,j] = jac_scaled[i,j]*sc
# delete dummy objective
if n_obj == 0:
delattr(m, dummy_objective_name)
return jac, jac_scaled, nlp
class CacheVars(object):
"""
A class for saving the values of variables then reloading them,
usually after they have been used to perform some solve or calculation.
"""
def __init__(self, vardata_list):
self.vars = vardata_list
self.cache = [None for var in self.vars]
def __enter__(self):
for i, var in enumerate(self.vars):
self.cache[i] = var.value
return self
def __exit__(self, ex_type, ex_value, ex_traceback):
for i, var in enumerate(self.vars):
var.set_value(self.cache[i])
class FlattenedScalingAssignment(object):
"""
A class to assist in the calculation of scaling factors when a
variable-constraint assignment can be constructed, especially when
the variables and constraints are all indexed by some common set(s).
"""
def __init__(self, scaling_factor, varconlist=[], nominal_index=()):
"""
Args:
scaling_factor: A Pyomo scaling_factor Suffix that will hold all
the scaling factors calculated
varconlist: A list of variable, constraint tuples. These variables
and constraints should be indexed by the same sets,
so they may need to be references-to-slices along some
common sets.
nominal_index: The index of variables and constraints to access
when a calculation needs to be performed using
data objects.
"""
self.scaling_factor = scaling_factor
self.nominal_index = nominal_index
if nominal_index is None or nominal_index == ():
self.dim = 0
else:
try:
self.dim = len(nominal_index)
except TypeError:
self.dim = 1
varlist = []
conlist = []
for var, con in varconlist:
varlist.append(var)
conlist.append(con)
self.varlist = varlist
self.conlist = conlist
data_getter = self.get_representative_data_object
var_con_data_list = [(data_getter(var), data_getter(con))
for var, con in varconlist]
con_var_data_list = [(data_getter(con), data_getter(var))
for var, con in varconlist]
self.var2con = ComponentMap(var_con_data_list)
self.con2var = ComponentMap(con_var_data_list)
def get_representative_data_object(self, obj):
"""
Gets a data object from an object of the appropriate dimension
"""
if self.dim == 0:
# In this way, obj can be a data object and this class can be
# used even if the assignment is not between "flattened components"
return obj
else:
nominal_index = self.nominal_index
return obj[nominal_index]
def calculate_variable_scaling_factor(self, var):
"""
Calculates the scaling factor of a variable based on the
constraint assigned to it. Loads each variable in that constraint
with its nominal value (inverse of scaling factor), calculates
the value of the target variable from the constraint, then sets
its scaling factor to the inverse of the calculated value.
"""
vardata = self.get_representative_data_object(var)
condata = self.var2con[vardata]
scaling_factor = self.scaling_factor
in_constraint = list(identify_variables(condata.expr))
source_vars = [v for v in in_constraint if v is not vardata]
nominal_source = [1/scaling_factor[var] for var in source_vars]
with CacheVars(in_constraint) as cache:
for v, nom_val in zip(source_vars, nominal_source):
v.set_value(nom_val)
# This assumes that target var is initialized to a somewhat
# reasonable value
calculate_variable_from_constraint(vardata, condata)
nominal_target = vardata.value
if nominal_target == 0:
target_factor = 1.0
else:
target_factor = abs(1/nominal_target)
if self.dim == 0:
scaling_factor[var] = target_factor
else:
for v in var.values():
scaling_factor[v] = target_factor
def set_constraint_scaling_factor(self, con):
"""
Sets the scaling factor of a constraint to that of its assigned variable
"""
condata = self.get_representative_data_object(con)
vardata = self.con2var[condata]
scaling_factor = self.scaling_factor
var_factor = scaling_factor[vardata]
if self.dim == 0:
scaling_factor[con] = var_factor
else:
for c in con.values():
scaling_factor[c] = var_factor
def set_derivative_factor_from_state(self, deriv, nominal_wrt=1.0):
"""
Sets the scaling factor for a DerivativeVar equal to the factor for
its state var at every index. This method needs access to the
get_state_var method, so deriv must be an actual DerivativeVar,
not a reference-to-slice.
"""
scaling_factor = self.scaling_factor
state_var = deriv.get_state_var()
for index, dv in deriv.items():
state_data = state_var[index]
nominal_state = 1/scaling_factor[state_data]
nominal_deriv = nominal_state/nominal_wrt
scaling_factor[dv] = 1/nominal_deriv
################################################################################
# DEPRECATED functions below.
################################################################################
def scale_single_constraint(c):
"""This transforms a constraint with its scaling factor. If there is no
scaling factor for the constraint, the constraint is not scaled and a
message is logged. After transforming the constraint the scaling factor,
scaling expression, and nomical value are all unset to ensure the constraint
isn't scaled twice.
Args:
c: Pyomo constraint
Returns:
None
"""
_log.warning(
"DEPRECATED: scale_single_constraint() will be removed and has no "
"direct replacement")
if not isinstance(c, _ConstraintData):
raise TypeError(
"{} is not a constraint and cannot be the input to "
"scale_single_constraint".format(c.name))
v = get_scaling_factor(c)
if v is None:
_log.warning(
f"{c.name} constraint has no scaling factor, so it was not scaled.")
return
c.set_value(
(__none_mult(c.lower, v), __none_mult(c.body, v), __none_mult(c.upper, v)))
unset_scaling_factor(c)
def scale_constraints(blk, descend_into=True):
"""This scales all constraints with their scaling factor suffix for a model
or block. After scaling the constraints, the scaling factor and expression
for each constraint is set to 1 to avoid double scaling the constraints.
Args:
blk: Pyomo block
descend_into: indicates whether to descend into the other blocks on blk.
(default = True)
Returns:
None
"""
_log.warning(
"DEPRECATED: scale_single_constraint() will be removed and has no "
"direct replacement")
for c in blk.component_data_objects(pyo.Constraint, descend_into=False):
scale_single_constraint(c)
if descend_into:
for b in blk.component_objects(pyo.Block, descend_into=True):
for c in b.component_data_objects(pyo.Constraint, descend_into=False):
scale_single_constraint(c)