将循环结果保存在向量R中

Question

I run a loop:

N = 10
alpha = 0.05
sigma = 0.01
for (i in 0:N){
Vt10[i] = ((sigma^2)/(alpha^2))*((N-i)+(2/alpha))*exp(-alpha*(N-i))-(1/(2*alpha))*exp(-2*alpha*(N-i))-(3/(2*alpha))
}

However, Vt10 eventually outputs only 10 outcomes (doesn't include the first iteration, when i = 0 ). How can I create a vector that would include all 11 iterations?

Answer 1

Answer:

N = 10
alpha = 0.05
sigma = 0.01
Vt10 = numeric(11)  ## this!
for (i in 0:N){
Vt10[i+1] = ((sigma^2)/(alpha^2))*((N-i)+(2/alpha))*exp(-alpha*(N-i))-(1/(2*alpha))*exp(-2*alpha*(N-i))-(3/(2*alpha))
}

Also, you need Vt10[i+1] , because you loop from 0 to 10, while array index should be 1 to 11.

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Comment:

Your code looks like C code. Not only you start index from 0, but also you write a loop for this task.

Try:

N = 10
alpha = 0.05
sigma = 0.01
i = 0:10
Vt10 = ((sigma^2)/(alpha^2))*((N-i)+(2/alpha))*exp(-alpha*(N-i))-(1/(2*alpha))*exp(-2*alpha*(N-i))-(3/(2*alpha))

In this situation, there is no need to predefine a vector. R knows you are performing element-wise computation, and will automatically assign a length-11 vector for Vt10 .