Module cache 

Expression caching and memoization.

This module provides caching mechanisms for expensive operations like evaluation, simplification, and complex number operations.

Features

• EvalCache: Thread-safe cache for real-valued evaluation results with LRU eviction
• ComplexEvalCache: Thread-safe cache for complex-valued evaluations (quantum amplitudes)
• SimplificationCache: Cache for expression simplification results
• BatchEvalCache: Optimized for VQE optimization loops with parameter sweeps
• CachedEvaluator: Convenient wrapper with all caching features integrated
• ExpressionCache: Hash consing for structural sharing of expressions

Performance Benefits

Expression caching is critical for quantum computing applications:

• VQE/QAOA loops: Same expressions evaluated thousands of times with different parameters
• Gradient computation: Derivatives computed repeatedly during optimization
• Circuit simulation: Gate matrices cached after first computation

Example

use quantrs2_symengine_pure::cache::{CachedEvaluator, hash_params};
use quantrs2_symengine_pure::Expression;
use std::collections::HashMap;

let evaluator = CachedEvaluator::new();
let expr = Expression::symbol("x").sin();

// First evaluation computes the result
let mut params = HashMap::new();
params.insert("x".to_string(), 0.5);
let result1 = evaluator.eval(&expr, &params).unwrap();

// Second evaluation retrieves from cache
let result2 = evaluator.eval(&expr, &params).unwrap();
assert!((result1 - result2).abs() < 1e-10);

// Check hit rate
let stats = evaluator.stats();
println!("Cache hit rate: {:.1}%", stats.overall_hit_rate() * 100.0);

Structs

BatchEvalCache

Cache for batch evaluation results in VQE optimization loops.

CacheStats

Cache statistics

CachedEvaluator

An expression evaluator with integrated caching.

CombinedCacheStats

Combined statistics for all cache types

ComplexEvalCache

Thread-safe cache for complex number evaluation results.

EvalCache

Thread-safe cache for expression evaluation results with LRU eviction.

ExpressionCache

Hash consing for structural sharing of expressions

SimplificationCache

Thread-safe cache for expression simplification results.

Constants

DEFAULT_MAX_CACHE_SIZE

Default maximum cache size (entries)

Functions

compute_hash

Compute a hash for an expression

hash_complex_params

Compute a hash for complex parameters

hash_param_array

Compute a hash for a parameter array (for batch operations)

hash_params

Compute a hash for a set of real parameters