gunshi-project-ss/src/main/java/com/gunshi/project/hsz/model/RegressionEquation.java

package com.gunshi.project.hsz.model;

import lombok.Data;

import java.math.BigDecimal;
import java.util.List;

/**
 * 线性回归方程实体类
 */
@Data
public class RegressionEquation {
    /**
     * 方程阶数
     */
    private int order;

    /**
     * 方程系数（从常数项到最高次项）
     * 例如：对于二次方程 y = ax² + bx + c，coefficients = [c, b, a]
     */
    private List<BigDecimal> coefficients;

    /**
     * 相关系数 R²
     */
    private BigDecimal rSquared;

    /**
     * 数据点数
     */
    private int dataCount;

    /**
     * 方程字符串表示
     */
    private String equationString;

    public RegressionEquation(int order, List<BigDecimal> coefficients, BigDecimal rSquared, int dataCount) {
        this.order = order;
        this.coefficients = coefficients;
        this.rSquared = rSquared;
        this.dataCount = dataCount;
        this.equationString = generateEquationString();
    }

    /**
     * 生成方程字符串
     */
    private String generateEquationString() {
        StringBuilder sb = new StringBuilder("y = ");

        for (int i = coefficients.size() - 1; i >= 0; i--) {
            BigDecimal coeff = coefficients.get(i);
            if (coeff.compareTo(BigDecimal.ZERO) == 0) {
                continue;
            }

            // 符号处理
            if (sb.length() > 4 && coeff.compareTo(BigDecimal.ZERO) > 0) {
                sb.append(" + ");
            } else if (sb.length() > 4 && coeff.compareTo(BigDecimal.ZERO) < 0) {
                sb.append(" - ");
                coeff = coeff.abs();
            }

            // 系数和变量
            if (i == 0) {
                // 常数项
                sb.append(String.format("%.4f", coeff));
            } else {
                // 非常数项
                if (coeff.compareTo(BigDecimal.ONE) != 0 && coeff.compareTo(BigDecimal.ONE.negate()) != 0) {
                    sb.append(String.format("%.4f", coeff));
                }
                sb.append("x");
                if (i > 1) {
                    sb.append("^").append(i);
                }
            }
        }

        return sb.toString();
    }

    /**
     * 根据x值预测y值
     */
    public BigDecimal predict(BigDecimal x) {
        BigDecimal result = BigDecimal.ZERO;
        BigDecimal xPower = BigDecimal.ONE;

        for (int i = 0; i < coefficients.size(); i++) {
            result = result.add(coefficients.get(i).multiply(xPower));
            xPower = xPower.multiply(x);
        }

        return result;
    }


    @Override
    public String toString() {
        return String.format("%s", equationString);
    }
}