quantrs2_tytan/sampler/hardware/

fujitsu.rs

//! Fujitsu Digital Annealer integration
//!
//! This module provides integration with Fujitsu's Digital Annealer,
//! a quantum-inspired optimization processor.

use crate::sampler::{SampleResult, Sampler, SamplerError, SamplerResult};
use scirs2_core::ndarray::Array2;
use std::collections::HashMap;
use std::time::Duration;

/// Fujitsu Digital Annealer configuration
#[derive(Debug, Clone)]
pub struct FujitsuConfig {
    /// API endpoint
    pub endpoint: String,
    /// API key
    pub api_key: String,
    /// Annealing time in milliseconds
    pub annealing_time: u32,
    /// Number of replicas
    pub num_replicas: u32,
    /// Offset increment
    pub offset_increment: f64,
    /// Temperature start
    pub temperature_start: f64,
    /// Temperature end
    pub temperature_end: f64,
    /// Temperature mode
    pub temperature_mode: TemperatureMode,
}

#[derive(Debug, Clone)]
pub enum TemperatureMode {
    /// Linear temperature schedule
    Linear,
    /// Exponential temperature schedule
    Exponential,
    /// Adaptive temperature schedule
    Adaptive,
}

impl Default for FujitsuConfig {
    fn default() -> Self {
        Self {
            endpoint: "https://api.da.fujitsu.com/v2".to_string(),
            api_key: String::new(),
            annealing_time: 1000,
            num_replicas: 16,
            offset_increment: 100.0,
            temperature_start: 1000.0,
            temperature_end: 0.1,
            temperature_mode: TemperatureMode::Exponential,
        }
    }
}

/// Fujitsu Digital Annealer sampler
pub struct FujitsuDigitalAnnealerSampler {
    config: FujitsuConfig,
    /// Maximum problem size
    max_variables: usize,
    /// Connectivity constraints
    connectivity: ConnectivityType,
}

#[derive(Debug, Clone)]
pub enum ConnectivityType {
    /// Fully connected
    FullyConnected,
    /// King's graph connectivity
    KingsGraph,
    /// Chimera graph connectivity
    Chimera { unit_size: usize },
}

impl FujitsuDigitalAnnealerSampler {
    /// Create new Fujitsu Digital Annealer sampler
    pub const fn new(config: FujitsuConfig) -> Self {
        Self {
            config,
            max_variables: 8192, // Current DA3 limit
            connectivity: ConnectivityType::FullyConnected,
        }
    }

    /// Set connectivity type
    pub const fn with_connectivity(mut self, connectivity: ConnectivityType) -> Self {
        self.connectivity = connectivity;
        self
    }

    /// Submit problem to Digital Annealer
    fn submit_problem(&self, _qubo: &Array2<f64>) -> Result<String, SamplerError> {
        // In a real implementation, this would:
        // 1. Format QUBO for DA API
        // 2. Submit via HTTP POST
        // 3. Return job ID

        // Placeholder implementation
        Ok("job_12345".to_string())
    }

    /// Poll for results
    fn get_results(
        &self,
        _job_id: &str,
        _timeout: Duration,
    ) -> Result<Vec<DASolution>, SamplerError> {
        // In a real implementation, this would:
        // 1. Poll the API for job completion
        // 2. Parse results
        // 3. Return solutions

        // Placeholder implementation
        Ok(vec![DASolution {
            configuration: vec![0; self.max_variables],
            energy: -100.0,
            frequency: 10,
        }])
    }

    /// Convert DA solution to sample result
    fn to_sample_result(
        &self,
        solution: &DASolution,
        var_map: &HashMap<String, usize>,
    ) -> SampleResult {
        let mut assignments = HashMap::new();

        for (var_name, &index) in var_map {
            if index < solution.configuration.len() {
                assignments.insert(var_name.clone(), solution.configuration[index] == 1);
            }
        }

        SampleResult {
            assignments,
            energy: solution.energy,
            occurrences: solution.frequency as usize,
        }
    }
}

/// Digital Annealer solution format
#[derive(Debug, Clone)]
struct DASolution {
    /// Binary configuration
    configuration: Vec<u8>,
    /// Solution energy
    energy: f64,
    /// Occurrence frequency
    frequency: u32,
}

impl Sampler for FujitsuDigitalAnnealerSampler {
    fn run_qubo(
        &self,
        model: &(Array2<f64>, HashMap<String, usize>),
        shots: usize,
    ) -> SamplerResult<Vec<SampleResult>> {
        let (qubo, var_map) = model;

        // Check problem size
        if qubo.shape()[0] > self.max_variables {
            return Err(SamplerError::InvalidModel(format!(
                "Problem size {} exceeds Digital Annealer limit of {}",
                qubo.shape()[0],
                self.max_variables
            )));
        }

        // Submit problem
        let job_id = self.submit_problem(qubo)?;

        // Get results
        let timeout = Duration::from_millis(self.config.annealing_time as u64 + 5000);
        let da_solutions = self.get_results(&job_id, timeout)?;

        // Convert to sample results
        let mut results: Vec<SampleResult> = da_solutions
            .iter()
            .map(|sol| self.to_sample_result(sol, var_map))
            .collect();

        // Sort by energy
        results.sort_by(|a, b| {
            a.energy
                .partial_cmp(&b.energy)
                .unwrap_or(std::cmp::Ordering::Equal)
        });

        // Limit to requested shots
        results.truncate(shots);

        Ok(results)
    }

    fn run_hobo(
        &self,
        hobo: &(scirs2_core::ndarray::ArrayD<f64>, HashMap<String, usize>),
        shots: usize,
    ) -> SamplerResult<Vec<SampleResult>> {
        let (tensor, var_map) = hobo;

        // Quadratize HOBO → QUBO via Rosenberg reduction.
        let (qubo, ext_var_map) = crate::sampler::energy::hobo_to_qubo(tensor, var_map)
            .map_err(SamplerError::InvalidModel)?;

        // Enforce Fujitsu Digital Annealer variable limit.
        if qubo.shape()[0] > self.max_variables {
            return Err(SamplerError::InvalidModel(format!(
                "HOBO quadratization produced {} variables, which exceeds Fujitsu Digital Annealer limit of {}",
                qubo.shape()[0],
                self.max_variables
            )));
        }

        // Delegate to the QUBO solver.
        let mut results = self.run_qubo(&(qubo, ext_var_map), shots)?;

        // Strip auxiliary variables (introduced by quadratization) from every result.
        for result in &mut results {
            result.assignments.retain(|k, _| !k.starts_with("_aux_"));
        }

        Ok(results)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_fujitsu_config() {
        let mut config = FujitsuConfig::default();
        assert_eq!(config.annealing_time, 1000);
        assert_eq!(config.num_replicas, 16);
    }

    #[test]
    fn test_connectivity_types() {
        let sampler = FujitsuDigitalAnnealerSampler::new(FujitsuConfig::default())
            .with_connectivity(ConnectivityType::KingsGraph);

        match sampler.connectivity {
            ConnectivityType::KingsGraph => (),
            _ => panic!("Wrong connectivity type"),
        }
    }
}