12 (a) Write a function, Power(), that prints out the result of raising 2 to the 3rd power. In other words, your function should compute $2^3$ and print out the results. Hint: Recall that $x^a$ raises x to the power a. Use the print() function to output the result.



In [9]:

    
Power = function(){
    print(2^3)
}

Power()

12 (b) Create a new function, Power2(), that allows you to pass any two numbers, x and a, and prints out the value of x^a. You can do this by beginning your function with the line:

> Power2=function(x,a){

You should be able to call your function by entering, for instance,

> Power2 (3 ,8)

on the command line. This should output the value of $3^8$, namely, $6, 561$.



In [10]:

    
Power2 = function(x, a){
    print(x^a)
}

Power2(3, 8)

12 (c) Using the Power2() function that you just wrote, compute $10^3$, $8^{17}$, and $131^3$.



In [11]:

    
Power2(10, 3)
Power2(8, 17)
Power2(131, 3)









    



[1] 1000
[1] 2.2518e+15
[1] 2248091

12 (d) Now create a new function, Power3(), that actually returns the result x^a as an R object, rather than simply printing it to the screen. That is, if you store the value x^a in an object called result within your function, then you can simply return() this result, using the following line:

return(result)

The line above should be the last line in your function, before the } symbol.



In [12]:

    
Power3 = function(x, a){
    result = x^a
    return (result)
}

print(Power3(3, 8))

12 (e) Now using the Power3() function, create a plot of $f(x) = x^2$. The x-axis should display a range of integers from 1 to 10, and the y-axis should display $x^2$. Label the axes appropriately, and use an appropriate title for the figure. Consider displaying either the x-axis, the y-axis, or both on the log-scale. You can do this by using log=‘‘x’’, log=‘‘y’’, or log=‘‘xy’’ as arguments to the plot() function.



In [30]:

    
x = 1:10
y = Power3(x,2)
par(mfrow=c(2,2))
plot(x, y, log="", xlab="x", ylab="y")
plot(x, y, log="x",  xlab="log(x)", ylab="y")
plot(x, y, log="y",  xlab="x", ylab="log(y)")
plot(x, y, log="xy", xlab="log(x)", ylab="log(y)")

12 (f) Create a function, PlotPower(), that allows you to create a plot of x against x^a for a fixed a and for a range of values of x. For instance, if you call

> PlotPower (1:10 ,3)

then a plot should be created with an x-axis taking on values 1,2,...,10, and a y-axis taking on values $1^3,2^3,...,10^3$.



In [46]:

    
PlotPower = function(X, a){
    Y = Power3(X,a)
    plot(X, Y, xlab="x", ylab="y", main=paste("y = x^",a))
}

par(mfrow=c(2,2))
X = 1:10
PlotPower(X, 3)

X = 30:50
PlotPower(X, 4)

X = 50:100
PlotPower(X, 6)

X = 10:115
PlotPower(X, 7)