Normal distribution R base

[bustosmiguel]

Hi,

How can I fill in the correct form the area?

Thanks

     f <- dnorm(x, Mean, Sd) # Density function
     qnorm(0.5, mean = 0, sd = 1) # 0
      x <- pnorm(-1.5, mean = 0, sd = 1) # 0.0668072
      qnorm(x, mean = 0, sd = 1) # -1.5
      
      Mean <- 0
      Sd <- 1
      # Area:
      lb <- -3 # Lower bound
      ub <- -1.5
      
      
                  x <- seq(-3, 3, length = 100) * Sd + Mean
                  x2 <- seq(min(x), ub, length = 0.2) # New Grid
                  y <- dnorm(x2, Mean, Sd) # Density
      
      # Plot Area:
      plot(x, f, type = "l", lwd = 2, col = "blue", ylab = "", xlab = "Weight", main = "")
      polygon(c(lb, x2, ub), c(0, y, 0), col = rgb(0, 0, 1, alpha = 0.5))

With that code, I obtain this:

How to fix it correctly?

[startz]

What are you trying to do? Do you want to shade part of the area under the bell curve?

[bustosmiguel]

Hi, yes.

I´ve been studying dnorm(), pnorm(), qnorm() and rnorm() in this website, an in that website there´s a solution with a function()

I don´t want to use the function, I want to understand the process, for that reason, I need that help.

thanks,

[startz]

Setting length = 0.2 in x2<-seq() is probably a mistake. Try changing that.

[bustosmiguel]

Here I added it but doesn´t work:

I´m so Sorry, this is the correct code, now you see the plot, that I sent at the beginning:

Mean <- 1000
Sd <- 10
x <- seq(-3, 3, length = 100) * Sd + Mean # X grid for non-standard normal distribution
f <- dnorm(x, Mean, Sd) # Density function
qnorm(0.5, mean = 0, sd = 1) # 0
x <- pnorm(-1.5, mean = 0, sd = 1) # 0.0668072
qnorm(x, mean = 0, sd = 1) # -1.5

Mean <- 0
Sd <- 1

lb <- -3 # Lower bound
ub <- -1.5

x <- seq(-3, 3, length = 100) * Sd + Mean
x2 <- seq(min(x), ub, length = 0.2) # New Grid
y <- dnorm(x2, Mean, Sd) # Density

plot(x, f, type = "l", lwd = 2, col = "blue", ylab = "", xlab = "Weight", main = "")
polygon(c(lb, x2, ub), c(0, y, 0), col = rgb(0, 0, 1, alpha = 0.5))

It must be a simple way, but i don´t know how to do that.
thanks,

[startz]

Part of the problem is that you are changing Mean and Sd. You also still have the length of x2 set to 0.2.

Could you tell us a little more about which parts of the code you understand and which parts you don't?

[bustosmiguel]

Now it works, with this code:

Sd <- 1
Mean <- 0 
x <- seq(-3, 3, length = 100) * Sd + Mean
x
lb <- -3
ub <- -1.5
x2 <- seq(lb, ub, length = 100) 
f <- dnorm(x, Mean, Sd) # Density function
y <- dnorm(x2, Mean, Sd) # Density


plot(x, f, type = "l", lwd = 2, col = "blue", ylab = "", xlab = "Weight", main = "")
polygon(c(lb, x2, ub), c(0, y, 0), col = rgb(0, 0, 1, alpha = 0.5))

Thanks for all the advices, now I have to practice more

Greetings,