Legacy Code.
Modern Solutions.

@Service
@Slf4j
public class InterestCalculationService {

    private final AccountRepository accountRepository;
    private final InterestAuditRepository auditRepository;

    @Transactional
    @Scheduled(cron = "0 0 2 * * *") // Nightly at 02:00
    public InterestRunResult calculateNightlyInterest() {
        LocalDate today = LocalDate.now();
        var result = new InterestRunResult();

        List<Account> eligibleAccounts = accountRepository
            .findByStatusAndTypeIn(
                AccountStatus.ACTIVE,
                List.of(AccountType.SAVINGS, AccountType.FIXED_DEPOSIT)
            );

        for (Account account : eligibleAccounts) {
            try {
                BigDecimal interest = calculateInterest(account, today);
                account.setBalance(account.getBalance().add(interest));
                account.setLastCalculationDate(today);
                accountRepository.save(account);

                auditRepository.save(InterestAudit.builder()
                    .accountNumber(account.getAccountNumber())
                    .interestAmount(interest)
                    .balanceAfter(account.getBalance())
                    .calculationDate(today)
                    .build());

                result.addProcessed(interest);
            } catch (Exception e) {
                log.error("Failed for account {}: {}",
                    account.getAccountNumber(), e.getMessage());
                result.addFailed();
            }
        }
        return result;
    }

    private BigDecimal calculateInterest(Account account, LocalDate today) {
        long daysElapsed = ChronoUnit.DAYS.between(
            account.getLastCalculationDate(), today);
        BigDecimal dailyRate = account.getInterestRate()
            .divide(BigDecimal.valueOf(365), 10, RoundingMode.HALF_UP);
        return account.getBalance()
            .multiply(dailyRate)
            .multiply(BigDecimal.valueOf(daysElapsed))
            .setScale(2, RoundingMode.HALF_UP);
    }
}

// ClaimSubmissionService.cs
public class ClaimSubmissionService : IClaimSubmissionService
{
    private readonly AppDbContext _db;
    private readonly IDocumentStorageService _documents;
    private readonly IReserveCalculator _reserveCalc;
    private readonly IValidator<ClaimSubmissionRequest> _validator;
    private readonly ILogger<ClaimSubmissionService> _logger;

    public async Task<ClaimResult> SubmitClaimAsync(
        ClaimSubmissionRequest request,
        ClaimsPrincipal user)
    {
        var validation = await _validator.ValidateAsync(request);
        if (!validation.IsValid)
            return ClaimResult.ValidationFailed(validation.Errors);

        await using var transaction = await _db.Database
            .BeginTransactionAsync();
        try
        {
            var claim = new Claim
            {
                PolicyNumber = request.PolicyNumber,
                ClaimDate = request.ClaimDate,
                Type = request.ClaimType,
                Amount = request.Amount,
                AdjusterId = user.GetAdjusterId(),
                Status = ClaimStatus.New,
                SubmittedAt = DateTimeOffset.UtcNow
            };
            _db.Claims.Add(claim);
            await _db.SaveChangesAsync();

            foreach (var doc in request.Documents)
                await _documents.StoreAsync(claim.Id, doc);

            claim.ReserveAmount = _reserveCalc.Calculate(
                claim.Type, claim.Amount);
            await _db.SaveChangesAsync();
            await transaction.CommitAsync();

            _logger.LogInformation(
                "Claim {ClaimId} submitted, reserve: {Reserve:C}",
                claim.Id, claim.ReserveAmount);

            return ClaimResult.Success(claim.Id, claim.ReserveAmount);
        }
        catch (Exception ex)
        {
            await transaction.RollbackAsync();
            _logger.LogError(ex, "Failed to submit claim");
            throw;
        }
    }
}

// ReserveCalculator.cs
public class ReserveCalculator : IReserveCalculator
{
    private static readonly Dictionary<ClaimType, decimal> Multipliers = new()
    {
        [ClaimType.AutoCollision]    = 1.15m,
        [ClaimType.AutoLiability]    = 1.50m,
        [ClaimType.PropertyFire]     = 1.25m,
        [ClaimType.PropertyWater]    = 1.10m,
        [ClaimType.LiabilityGeneral] = 2.00m,
    };

    public decimal Calculate(ClaimType type, decimal amount) =>
        amount * Multipliers.GetValueOrDefault(type, 1.20m);
}

"""2D Heat Transfer Simulation — Finite Difference Method."""

import numpy as np
from dataclasses import dataclass
from pathlib import Path
import logging

logger = logging.getLogger(__name__)


@dataclass
class SimulationConfig:
    nx: int = 100
    ny: int = 100
    alpha: float = 0.01
    t_max: float = 1.0
    boundary_left: float = 100.0
    boundary_right: float = 0.0
    boundary_top: float = 0.0
    boundary_bottom: float = 0.0
    initial_temp: float = 25.0


class HeatSimulation2D:
    def __init__(self, config: SimulationConfig):
        self.config = config
        self.dx = 1.0 / (config.nx - 1)
        self.dt = 0.25 * self.dx**2 / config.alpha
        self.n_steps = int(config.t_max / self.dt)
        self.r = config.alpha * self.dt / self.dx**2
        self.grid = self._initialize_grid()

    def _initialize_grid(self) -> np.ndarray:
        grid = np.full(
            (self.config.nx, self.config.ny),
            self.config.initial_temp
        )
        grid[0, :] = self.config.boundary_left
        grid[-1, :] = self.config.boundary_right
        grid[:, 0] = self.config.boundary_bottom
        grid[:, -1] = self.config.boundary_top
        return grid

    def run(self, log_interval: int = 1000) -> np.ndarray:
        logger.info("Starting: %d steps, grid %dx%d",
            self.n_steps, self.config.nx, self.config.ny)

        for step in range(1, self.n_steps + 1):
            interior = self.grid[1:-1, 1:-1]
            neighbors = (
                self.grid[2:, 1:-1] + self.grid[:-2, 1:-1] +
                self.grid[1:-1, 2:] + self.grid[1:-1, :-2]
            )
            new_interior = interior + self.r * (neighbors - 4 * interior)
            max_diff = np.max(np.abs(new_interior - interior))
            self.grid[1:-1, 1:-1] = new_interior

            if step % log_interval == 0:
                logger.info("Step %d / %d — max diff: %.5e",
                    step, self.n_steps, max_diff)

        return self.grid

    def save(self, path: Path) -> None:
        x = np.linspace(0, 1, self.config.nx)
        y = np.linspace(0, 1, self.config.ny)
        xx, yy = np.meshgrid(x, y, indexing='ij')
        data = np.column_stack([xx.ravel(), yy.ravel(), self.grid.ravel()])
        np.savetxt(path, data, fmt='%10.6f %10.6f %12.6f')
        logger.info("Results saved to %s", path)


if __name__ == "__main__":
    logging.basicConfig(level=logging.INFO)
    sim = HeatSimulation2D(SimulationConfig())
    sim.run()
    sim.save(Path("heat_output.dat"))