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Expression Simplifier

SRToolkit.utils.expression_simplifier

simplify 

simplify(expr: Union[List[str], Node], symbol_library: SymbolLibrary = SymbolLibrary.default_symbols()) -> Union[List[str], Node]
Simplifies a mathematical expression by
  1. Making use of sympy's simplification functions
  2. Simplifying constants, e.g. C*C + C -> C

Examples:

>>> expr = ["C", "+", "C" "*", "C", "+", "X_0", "*", "X_1", "/", "X_0"]
>>> print("".join(simplify(expr)))
C+X_1

Parameters:

Name Type Description Default
expr Union[List[str], Node]

The expression given as a list of tokens in the infix notation or as an instance of SRToolkit.utils.expression_tree.Node

 required
symbol_library SymbolLibrary

The symbol library to use. Defaults to SymbolLibrary.default_symbols().

 default_symbols()

Raises:

Type Description
Exception

If problems occur during simplification or if the expression contains invalid symbols.

Returns:

Type Description
Union[List[str], Node]

The simplified expression
Source code in SRToolkit/utils/expression_simplifier.py 
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def simplify(
    expr: Union[List[str], Node],
    symbol_library: SymbolLibrary = SymbolLibrary.default_symbols(),
) -> Union[List[str], Node]:
    """
    Simplifies a mathematical expression by:
        1. Making use of sympy's simplification functions
        2. Simplifying constants, e.g. C*C + C -> C

    Examples:
        >>> expr = ["C", "+", "C" "*", "C", "+", "X_0", "*", "X_1", "/", "X_0"]
        >>> print("".join(simplify(expr)))
        C+X_1

    Args:
        expr: The expression given as a list of tokens in the infix notation or as an instance of SRToolkit.utils.expression_tree.Node
        symbol_library: The symbol library to use. Defaults to SymbolLibrary.default_symbols().

    Raises:
        Exception: If problems occur during simplification or if the expression contains invalid symbols.

    Returns:
        The simplified expression
    """
    is_tree = False
    if isinstance(expr, Node):
        expr = expr.to_list(symbol_library=symbol_library, notation="infix")
        is_tree = True

    variables = symbol_library.get_symbols_of_type("var")

    # We expect only one symbol for constants
    if len(symbol_library.get_symbols_of_type("const")) > 0:
        constant = symbol_library.get_symbols_of_type("const")[0]
    else:
        # In this case constants shouldn't be problematic as they are not in the SymbolLibrary
        # Just in case and to not change other functions, I changed it to __C__.
        constant = "__C__"

    expr = _simplify_expression("".join(expr), constant, variables)
    expr = sympify(_denumerate_constants(str(expr), constant), evaluate=False)
    expr = _sympy_to_sr(expr)
    if not _check_tree(expr, symbol_library):
        raise Exception(
            "Simplified expression contains invalid symbols. Possibly skip its simplification or add symbols to the SymbolLibrary."
        )

    if is_tree:
        return expr
    else:
        return expr.to_list(symbol_library=symbol_library, notation="infix")