我尝试使用 lm() 和 poly() 来计算最佳拟合二阶多项式曲线。运行良好，但是当我使用lines() 绘制它时，曲线看起来很奇怪，好像在图表上绘制了多条曲线。
play <- filtered_file[filtered_file$`Rating to Use` == "A" & filtered_file$`INDUSTRY_GROUP/BCLASS2` == "Supranational", ]
play<- select(play,c(`Barclays New`,`Days_till_maturity` ) )
plot(play$`Barclays New` ~ play$`Days_till_maturity`)
linear <- lm( play$`Barclays New` ~ play$`Days_till_maturity`)
polynomial_2 <- lm( play$`Barclays New` ~ poly(play$`Days_till_maturity`,2, raw = TRUE) )
polynomial_3 <- lm( play$`Barclays New` ~ poly(play$`Days_till_maturity`,3, raw = TRUE) )
lines(play$`Days_till_maturity`, predict(linear), col = "blue" )
lines(play$`Days_till_maturity`, predict(polynomial_2), col = "red" )
lines(play$`Days_till_maturity`, predict(polynomial_3), col = "green" )
图表显示多条蓝色直线（相互重叠）和许多红色曲线
