Assignment Collection & Simplifications¶
AssignmentCollection¶

class
AssignmentCollection
(main_assignments, subexpressions={}, simplification_hints=None, subexpression_symbol_generator=None)¶ A collection of equations with subexpression definitions, also represented as assignments, that are used in the main equations. AssignmentCollection can be passed to simplification methods. These simplification methods can change the subexpressions, but the number and left hand side of the main equations themselves is not altered. Additionally a dictionary of simplification hints is stored, which are set by the functions that create assignment collections to transport information to the simplification system.

main_assignments
¶ list of assignments

subexpressions
¶ list of assignments defining subexpressions used in main equations

simplification_hints
¶ dict that is used to annotate the assignment collection with hints that are used by the simplification system. See documentation of the simplification rules for potentially required hints and their meaning.

subexpression_symbol_generator
¶ generator for new symbols that are used when new subexpressions are added used to get new symbols that are unique for this AssignmentCollection

add_simplification_hint
(key, value)¶ Adds an entry to the simplification_hints dictionary and checks that is does not exist yet.
 Return type

add_subexpression
(rhs, lhs=None, topological_sort=True)¶ Adds a subexpression to current collection.
 Parameters
rhs (
Expr
) – right hand side of new subexpressionlhs (
Optional
[Symbol
]) – optional left hand side of new subexpression. If None a new unique symbol is generated.topological_sort – sort the subexpressions topologically after insertion, to make sure that definition of a symbol comes before its usage. If False, subexpression is appended.
 Return type
 Returns
left hand side symbol (which could have been generated)

topological_sort
(sort_subexpressions=True, sort_main_assignments=True)¶ Sorts subexpressions and/or main_equations topologically to make sure symbol usage comes after definition.
 Return type

property
all_assignments
¶ Subexpression and main equations as a single list.
 Return type

property
free_symbols
¶ All symbols used in the assignment collection, which do not occur as left hand sides in any assignment.

property
bound_symbols
¶ All symbols which occur on the left hand side of a main assignment or a subexpression.

property
free_fields
¶ All fields accessed in the assignment collection, which do not occur as left hand sides in any assignment.

property
bound_fields
¶ All field accessed on the left hand side of a main assignment or a subexpression.

property
defined_symbols
¶ All symbols which occur as lefthandsides of one of the main equations

property
operation_count
¶ See
count_operations()

dependent_symbols
(symbols)¶ Returns all symbols that depend on one of the passed symbols.
A symbol ‘a’ depends on a symbol ‘b’, if there is an assignment ‘a < some_expression(b)’ i.e. when ‘b’ is required to compute ‘a’.

lambdify
(symbols, fixed_symbols=None, module=None)¶ Returns a python function to evaluate this equation collection.
 Parameters
Examples
>>> a, b, c, d = sp.symbols("a b c d") >>> ac = AssignmentCollection([Assignment(c, a + b), Assignment(d, a**2 + b)], ... subexpressions=[Assignment(b, a + b / 2)]) >>> python_function = ac.lambdify([a], fixed_symbols={b: 2}) >>> python_function(4) {c: 6, d: 18}

copy
(main_assignments=None, subexpressions=None)¶ Returns a copy with optionally replaced main_assignments and/or subexpressions.
 Return type
AssignmentCollection

new_with_substitutions
(substitutions, add_substitutions_as_subexpressions=False, substitute_on_lhs=True, sort_topologically=True)¶ Returns new object, where terms are substituted according to the passed substitution dict.
 Parameters
substitutions (
Dict
) – dict that is passed to sympy subs, substitutions are done main assignments and subexpressionsadd_substitutions_as_subexpressions (
bool
) – if True, the substitutions are added as assignments to subexpressionssubstitute_on_lhs (
bool
) – if False, the substitutions are done only on the right hand side of assignmentssort_topologically (
bool
) – if subexpressions are added as substitutions and this parameters is true, the subexpressions are sorted topologically after insertion
 Return type
AssignmentCollection
 Returns
New AssignmentCollection where substitutions have been applied, self is not altered.

new_merged
(other)¶ Returns a new collection which contains self and other. Subexpressions are renamed if they clash.
 Return type
AssignmentCollection

new_filtered
(symbols_to_extract)¶ Extracts equations that have symbols_to_extract as left hand side, together with necessary subexpressions.
 Return type
AssignmentCollection
 Returns
new AssignmentCollection, self is not altered

new_without_unused_subexpressions
()¶ Returns new collection that only contains subexpressions required to compute the main assignments.
 Return type
AssignmentCollection

new_with_inserted_subexpression
(symbol)¶ Eliminates the subexpression with the given symbol on its left hand side, by substituting it everywhere.
 Return type
AssignmentCollection

new_without_subexpressions
(subexpressions_to_keep={})¶ Returns a new collection where all subexpressions have been inserted.
 Return type
AssignmentCollection

Simplifications¶

class
AssignmentCollection
(main_assignments, subexpressions={}, simplification_hints=None, subexpression_symbol_generator=None)¶ A collection of equations with subexpression definitions, also represented as assignments, that are used in the main equations. AssignmentCollection can be passed to simplification methods. These simplification methods can change the subexpressions, but the number and left hand side of the main equations themselves is not altered. Additionally a dictionary of simplification hints is stored, which are set by the functions that create assignment collections to transport information to the simplification system.

main_assignments
¶ list of assignments

subexpressions
¶ list of assignments defining subexpressions used in main equations

simplification_hints
¶ dict that is used to annotate the assignment collection with hints that are used by the simplification system. See documentation of the simplification rules for potentially required hints and their meaning.

subexpression_symbol_generator
¶ generator for new symbols that are used when new subexpressions are added used to get new symbols that are unique for this AssignmentCollection

add_simplification_hint
(key, value)¶ Adds an entry to the simplification_hints dictionary and checks that is does not exist yet.
 Return type

add_subexpression
(rhs, lhs=None, topological_sort=True)¶ Adds a subexpression to current collection.
 Parameters
rhs (
Expr
) – right hand side of new subexpressionlhs (
Optional
[Symbol
]) – optional left hand side of new subexpression. If None a new unique symbol is generated.topological_sort – sort the subexpressions topologically after insertion, to make sure that definition of a symbol comes before its usage. If False, subexpression is appended.
 Return type
 Returns
left hand side symbol (which could have been generated)

topological_sort
(sort_subexpressions=True, sort_main_assignments=True)¶ Sorts subexpressions and/or main_equations topologically to make sure symbol usage comes after definition.
 Return type

property
all_assignments
¶ Subexpression and main equations as a single list.
 Return type

property
free_symbols
¶ All symbols used in the assignment collection, which do not occur as left hand sides in any assignment.

property
bound_symbols
¶ All symbols which occur on the left hand side of a main assignment or a subexpression.

property
free_fields
¶ All fields accessed in the assignment collection, which do not occur as left hand sides in any assignment.

property
bound_fields
¶ All field accessed on the left hand side of a main assignment or a subexpression.

property
defined_symbols
¶ All symbols which occur as lefthandsides of one of the main equations

property
operation_count
¶ See
count_operations()

dependent_symbols
(symbols)¶ Returns all symbols that depend on one of the passed symbols.
A symbol ‘a’ depends on a symbol ‘b’, if there is an assignment ‘a < some_expression(b)’ i.e. when ‘b’ is required to compute ‘a’.

lambdify
(symbols, fixed_symbols=None, module=None)¶ Returns a python function to evaluate this equation collection.
 Parameters
Examples
>>> a, b, c, d = sp.symbols("a b c d") >>> ac = AssignmentCollection([Assignment(c, a + b), Assignment(d, a**2 + b)], ... subexpressions=[Assignment(b, a + b / 2)]) >>> python_function = ac.lambdify([a], fixed_symbols={b: 2}) >>> python_function(4) {c: 6, d: 18}

copy
(main_assignments=None, subexpressions=None)¶ Returns a copy with optionally replaced main_assignments and/or subexpressions.
 Return type
AssignmentCollection

new_with_substitutions
(substitutions, add_substitutions_as_subexpressions=False, substitute_on_lhs=True, sort_topologically=True)¶ Returns new object, where terms are substituted according to the passed substitution dict.
 Parameters
substitutions (
Dict
) – dict that is passed to sympy subs, substitutions are done main assignments and subexpressionsadd_substitutions_as_subexpressions (
bool
) – if True, the substitutions are added as assignments to subexpressionssubstitute_on_lhs (
bool
) – if False, the substitutions are done only on the right hand side of assignmentssort_topologically (
bool
) – if subexpressions are added as substitutions and this parameters is true, the subexpressions are sorted topologically after insertion
 Return type
AssignmentCollection
 Returns
New AssignmentCollection where substitutions have been applied, self is not altered.

new_merged
(other)¶ Returns a new collection which contains self and other. Subexpressions are renamed if they clash.
 Return type
AssignmentCollection

new_filtered
(symbols_to_extract)¶ Extracts equations that have symbols_to_extract as left hand side, together with necessary subexpressions.
 Return type
AssignmentCollection
 Returns
new AssignmentCollection, self is not altered

new_without_unused_subexpressions
()¶ Returns new collection that only contains subexpressions required to compute the main assignments.
 Return type
AssignmentCollection

new_with_inserted_subexpression
(symbol)¶ Eliminates the subexpression with the given symbol on its left hand side, by substituting it everywhere.
 Return type
AssignmentCollection

new_without_subexpressions
(subexpressions_to_keep={})¶ Returns a new collection where all subexpressions have been inserted.
 Return type
AssignmentCollection


class
SimplificationStrategy
¶ A simplification strategy is an ordered collection of simplification rules.
Each simplification is a function taking an assignment collection, and returning a new simplified assignment collection. The strategy can nicely print intermediate simplification stages and results to Jupyter notebooks.

add
(rule)¶ Adds the given simplification rule to the end of the collection.

apply
(assignment_collection)¶ Runs all rules on the given assignment collection.
 Return type
AssignmentCollection

create_simplification_report
(assignment_collection)¶ Creates a report to be displayed as HTML in a Jupyter notebook.
The simplification report contains the number of operations at each simplification stage together with the runtime the simplification took.
 Return type

show_intermediate_results
(assignment_collection, symbols=None)¶ Shows the assignment collection after the application of each rule as HTML report for Jupyter notebook.


sympy_cse
(ac, **kwargs)¶ Searches for common subexpressions inside the assignment collection.
Searches is done in both the existing subexpressions as well as the assignments themselves. It uses the sympy subexpression detection to do this. Return a new assignment collection with the additional subexpressions found

sympy_cse_on_assignment_list
(assignments)¶ Extracts common subexpressions from a list of assignments.
 Return type

apply_to_all_assignments
(operation)¶ Applies a given operation to all equations in collection.

apply_on_all_subexpressions
(operation)¶ Applies the given operation on all subexpressions of the AC.

subexpression_substitution_in_existing_subexpressions
(ac)¶ Goes through the subexpressions list and replaces the term in the following subexpressions.

subexpression_substitution_in_main_assignments
(ac)¶ Replaces already existing subexpressions in the equations of the assignment_collection.

add_subexpressions_for_constants
(ac)¶ Extracts constant factors to subexpressions in the given assignment collection.
SymPy will exclude common factors from a sum only if they are symbols. This simplification can be applied to exclude common numeric constants from multiple terms of a sum. As a consequence, the number of multiplications is reduced and in some cases, more common subexpressions can be found.

add_subexpressions_for_divisions
(ac)¶ Introduces subexpressions for all divisions which have no constant in the denominator.
For example \(\frac{1}{x}\) is replaced while \(\frac{1}{3}\) is not replaced.

add_subexpressions_for_sums
(ac)¶ Introduces subexpressions for all sums  i.e. splits addends into subexpressions.

add_subexpressions_for_field_reads
(ac, subexpressions=True, main_assignments=True)¶ Substitutes field accesses on rhs of assignments with subexpressions
Can change semantics of the update rule (which is the goal of this transformation) This is useful if a field should be update in place  all values are loaded before into subexpression variables, then the new values are computed and written to the same field inplace.