R中的希腊字母

Question

我希望在不同参数alpha的相同图上有三条曲线。

curve(sin(x), from = 1, to = 3, lty = 1, ylim = c(-1, 1))
curve(sin(2 * x), add = TRUE, lty = 2)    
curve(sin(3 * x), add = TRUE, lty = 3)
legend("topright", legend = expression(paste(alpha, " = ", c(1, 2, 3))), lty = 1:3)

在图例中，我希望有三行alplha = 1，alpha = 2，alpha = 3.如何使其正确？

Answer 1

更好的循环答案来自here和user20650。

有蓝宝石的解决方案

expression函数非常棘手，但与substitute结合使用时，您可以使用sapply循环：

curve(sin(x), from = 1, to = 3, lty = 1, ylim = c(-1, 1))
curve(sin(2 * x), add = TRUE, lty = 2)    
curve(sin(3 * x), add = TRUE, lty = 3)
legend("topright",
       legend = sapply(1:3, function(x) as.expression(substitute(alpha == B,
                                                                 list(B = as.name(x))))),
       lty = 1:3)

简单修复

curve(sin(x), from = 1, to = 3, lty = 1, ylim = c(-1, 1))
curve(sin(2 * x), add = TRUE, lty = 2)    
curve(sin(3 * x), add = TRUE, lty = 3)
legend("topright", legend = c(expression(paste(alpha, " = ", 1)),
                              expression(paste(alpha, " = ", 2)),
                              expression(paste(alpha, " = ", 3))), lty = 1:3)