composite-resolve 0.1.6

Exact limit computation for Python functions. Resolve singularities algebraically.

composite-resolve

Evaluate Python functions at points where they're undefined.

Pass a plain numeric Python function and get exact limits via algebraic infinitesimal arithmetic. To my knowledge, this is the first library that does this directly on plain Python functions - no symbolic expressions, no approximation.

Note however, this is a mathematical correctness and continuity analysis tool, not a general execution safety mechanism. It is usefull for verifying the mathematical correctness of functions before they become production code.

It can only be used as general execution safety mechamism at runtime in some very limited and specific cases like in physics-style modeling and signal processing math (interpolation in DSP is the reason this tool emerged after all), but you have to know what you are doing in such cases.

Do not use use this as a general execution safety mechanism unless you are aware of consequences of using the limit results at the points where function is genuinely undefined.

import math
from composite_resolve import safe

@safe
def sinc(x):
    return math.sin(x) / x

sinc(0.5)  # → 0.9589 (normal computation)
sinc(0)    # → 1.0 (singularity resolved)

Uses composite arithmetic to resolve singularities algebraically. Works with any callable that uses standard Python arithmetic and math module functions. Pure Python, zero dependencies.

Install

pip install composite-resolve

The @safe Decorator

Write your math as-is. The decorator handles singularities automatically:

import math
from composite_resolve import safe

@safe
def f(x):
    return (x**2 - 1) / (x - 1)

f(3)   # → 4.0 (normal)
f(1)   # → 2.0 (resolved - no ZeroDivisionError)

@safe
def entropy(p):
    return -p * math.log(p)

entropy(0.5)  # → 0.347 (normal)
entropy(0)    # → 0.0 (resolved - no ValueError)

Normal inputs run the original function directly with zero overhead. Only when the function fails (ZeroDivisionError, NaN, Inf) does the resolver kick in.

Direct API

For more control, use resolve, limit, and classify directly:

import math
from composite_resolve import resolve, limit, classify, taylor

# Evaluate at removable singularities
resolve(lambda x: math.sin(x) / x, at=0)                # → 1.0
resolve(lambda x: (math.exp(x) - 1) / x, at=0)          # → 1.0
resolve(lambda x: (x**2 - 1) / (x - 1), at=1)           # → 2.0

# Indeterminate forms
limit(lambda x: x * math.log(x), to=0, dir="+")          # → 0.0    (0 × ∞)
limit(lambda x: x**x, to=0, dir="+")                      # → 1.0    (0⁰)
limit(lambda x: (1 + x)**(1/x), to=0)                     # → e      (1^∞)
limit(lambda x: 1/x - 1/math.sin(x), to=0)                # → 0.0    (∞ − ∞)

# Limits at infinity
limit(lambda x: (1 + 1/x)**x, to=math.inf)                # → e
limit(lambda x: math.sin(x) / x, to=math.inf)              # → 0.0

# One-sided limits
limit(lambda x: 1/x, to=0, dir="+")   # raises LimitDivergesError (+∞)
limit(lambda x: 1/x, to=0, dir="-")   # raises LimitDivergesError (-∞)
limit(lambda x: 1/x, to=0)            # raises LimitDoesNotExistError

# Singularity classification
classify(lambda x: math.sin(x)/x, at=0)   # → Removable(value=1.0)
classify(lambda x: 1/x, at=0)             # → Pole(order=1, residue=1.0)
classify(lambda x: math.exp(x), at=0)     # → Regular(value=1.0)

# Taylor coefficients
taylor(lambda x: math.exp(x), at=0, order=4)
# → [1.0, 1.0, 0.5, 0.16667, 0.04167]

How It Works

The library evaluates functions using composite arithmetic. Instead of symbolic manipulation, the library substitutes a concrete algebraic infinitesimal into your function. The result carries enough structure to resolve 0/0, 0×∞, and all other indeterminate forms through ordinary arithmetic.

The function is treated as a black box. No expression tree, no symbolic manipulation.

Evaluation layers

1. Fast path - f(float(to)) evaluated directly. If the point is regular (no singularity), this returns instantly. A continuity check at to ± ε prevents silent mis-evaluation at discontinuities.

2. Composite arithmetic - the core primitive. Substitutes a seeded composite number at the limit point and evaluates f through the full derivative tower. Handles removable singularities, indeterminate forms, and pole detection algebraically.

3. Numerical fallback - when composite arithmetic hits a representation it can't handle (e.g., ln(∞), floor at infinity, factorial overflow), falls back to evaluating f at nearby float probe points and extrapolating convergence/divergence.

4. Clear refusal - when none of the above can determine the answer, raises LimitUndecidableError (not LimitDoesNotExistError) to distinguish "we couldn't determine this" from "the limit genuinely does not exist. (I'm deliberating should I move this above numerical fallback and limit this library only to Composite resolvable limits. TBD.)"

API

safe(f) -> wrapped function

Decorator. Normal inputs run f directly. Singularities are resolved automatically.

resolve(f, at, dir="both", truncation=20) -> float

Evaluate f at a point where it would normally fail. Returns math.inf or -math.inf for divergent limits.

limit(f, to, dir="both", truncation=20) -> float

Compute the limit of f(x) as x → to. Raises:

• LimitDivergesError - limit is ±∞ (access .value for the sign)
• LimitDoesNotExistError - limit genuinely does not exist (oscillation, one-sided limits disagree). Carries evidence in .left_limit / .right_limit.
• LimitUndecidableError - CR could not determine the limit. The mathematical limit may still exist. Typical causes: double-precision overflow in probes, sub-polynomial growth rates the integer-dimension system can't represent, or expressions requiring log-space computation.

evaluate(f, at) -> float

Strict: only returns a value if the singularity is removable. Raises SingularityError otherwise.

taylor(f, at=0, order=10) -> list[float]

Extract Taylor coefficients [f(a), f'(a)/1!, f''(a)/2!, ...].

classify(f, at=0, dir="both") -> SingularityType

Returns Regular, Removable, Pole, or Essential.

residue(f, at=0) -> float

Residue at a pole.

Supported Math Functions

composite_resolve.math provides composite-aware versions of 42 functions. These accept both plain floats and Composite objects - use them in functions passed to limit()/resolve() for guaranteed composite propagation, or use math.* / numpy.* which are patched automatically during evaluation.

Core transcendentals: sin cos tan exp log ln sqrt

Inverse trig / hyperbolic: asin acos atan sinh cosh tanh asinh acosh atanh

Reciprocal trig / hyperbolic: cot sec csc coth sech csch

Inverse reciprocal: acot asec acsc asech acsch acoth

Early-cancellation primitives (numerically stable near cancellation points): expm1 (= exp(x)−1), log1p (= ln(1+x)), cosm1 (= cos(x)−1)

Step / piecewise (direction-aware at discontinuities): floor ceil ceiling frac

Arithmetic: cbrt (real cube root, handles negatives), Mod (mathematical modulo)

Error functions: erf erfc erfi

Fresnel integrals: fresnels fresnelc

Gamma family: gamma (with pole handling at 0, −1, −2, …), factorial, binomial

Not yet supported: Bessel functions (J, Y, I, K), exponential integral (Ei), Lambert W, elliptic integrals. These raise NameError if used in expressions passed to limit().

Examples

# Evaluate a function across its full domain, including singularities
from composite_resolve import resolve

f = lambda x: (x**2 - 1) / (x - 1)
for x in range(-5, 6):
    print(f"x={x:>2d}  f(x)={resolve(f, at=x):.1f}")
# x=1 gives 2.0 - no special case needed

# Cross-entropy loss at boundary
resolve(lambda p: -(0*math.log(p) + 1*math.log(1-p)), at=0, dir="+")  # → 0.0

# Continuous compounding
limit(lambda n: (1 + 0.05/n)**n, to=math.inf)  # → 1.05127

# Directional limits at discontinuities
from composite_resolve.math import floor, ceiling

limit(lambda x: floor(x), to=2, dir="+")   # → 2
limit(lambda x: floor(x), to=2, dir="-")   # → 1
limit(lambda x: ceiling(x), to=2, dir="+") # → 3

Math Library Support

Functions can use math, numpy, or composite_resolve.math - all work transparently:

import math
import numpy as np
from composite_resolve import safe

@safe
def f(x):
    return math.sin(x) / x    # works

@safe
def g(x):
    return np.sin(x) / x      # also works

f(0)  # → 1.0
g(0)  # → 1.0

math functions are patched during resolution. numpy functions dispatch via __array_ufunc__.

Important: use import math not from math import sin. The from form captures the original function at import time - patching the module later doesn't reach it.

Error Semantics

composite-resolve distinguishes three failure modes:

Error	Meaning	User action
LimitDivergesError	Limit is ±∞	Access .value for the sign
LimitDoesNotExistError	Limit genuinely doesn't exist - positive evidence (oscillation, one-sided limits disagree)	Check .left_limit / .right_limit for the one-sided values
LimitUndecidableError	CR couldn't determine the limit - no claim about existence	Try a symbolic engine (SymPy) or higher-precision tool (mpmath)

LimitUndecidableError is NOT a subclass of LimitDoesNotExistError. They represent fundamentally different situations: evidence of non-existence vs. insufficient machinery.

Limitations

• Single-variable functions only. Multi-variable limits are out of scope.
• Use import math not from math import sin - the from form captures the original function; patching can't reach it.
• Float-precision evaluation points. math.pi/2 is not exactly π/2 - limits at transcendental points may lose precision.
• Not thread-safe during limit()/resolve()/@safe calls (the math module is temporarily patched).
• Integer-dimension limitation. The composite number system uses integer dimensions. Functions whose growth rate sits between polynomial orders (like log(x), which grows slower than x^ε for any ε > 0) can't be faithfully represented. Limits involving log/polynomial rate comparisons may fall to numerical extrapolation or raise LimitUndecidableError.
• Double-precision overflow. Numerical fallback probes are plain Python floats. Functions like factorial(n) overflow at n > 170; exp(x) at x > 709. Limits requiring probe values beyond these ranges may be undecidable.
• Unsupported functions (jax, torch, Bessel, Ei, Lambert W, etc.) raise UnsupportedFunctionError or NameError - not silent wrong answers.

License

AGPL-3.0. Commercial licensing available: [e-mail]

Author

Toni Milovan - [e-mail]