Question

我正在尝试在R中构建一个函数，它表示范围为[0,1]的100Hz的方波和锯齿波。我试过这个：

squarewave <- function (t) {  

  # 0.01  == 100Hz(=2Pi) -> 1 Period of the Squarewave
  # 0.005 == Pi          -> Half Period of the Squarewave
  # if t smaller than a half period -> 1
  # if t greater or equal than half a period -> 0

  if ((t %% 0.01) < 0.005)
    return (1)
  else if ((t %% 0.01) >= 0.005)
    return (0)

}

当我尝试用以下函数绘制此函数时：

plot(squarewave)

我收到以下错误：

> plot(squarewave)
Error in curve(expr = x, from = from, to = to, xlim = xlim, ylab = ylab,  : 
  'expr' has not been evaluated to an object of length 'n'
In addition: Warning message:
In if ((t%%0.01) < 0.005) return(1) else if ((t%%0.01) >= 0.005) return(0) :
  the condition has length > 1 and only the first element will be used

那为什么这不起作用？

Answer 1

您需要将向量化函数传递给plot。因此，要么使用Vectorize自动执行此操作，要么使用ifelse代替if。

plot(Vectorize(squarewave))

或

squarewave2 <- function (t) {  

  # 0.01  == 100Hz(=2Pi) -> 1 Period of the Squarewave
  # 0.005 == Pi          -> Half Period of the Squarewave
  # if t smaller than a half period -> 1
  # if t greater or equal than half a period -> 0

  ifelse(((t %% 0.01) < 0.005),1,0)
}

plot(squarewave2)

要提高plot的分辨率，请使用参数n，有关详细信息，请参阅?curve。

Answer 2

我最初错了，想要更新。

除非它已正确矢量化，否则无法绘制原始函数，而是需要绘制函数的输出。下面是使用您的特定功能执行此操作的简单方法。

sequence <- seq(from = 0,to = 0.01, by = 0.00001)
plot(sapply(X = sequence,FUN = squarewave),type = "o")

编程方波＆amp; R中的锯齿波

2 个答案: