[英]Calculating derivative at values in a list
I have a function, say f = f(x) 我有一个函数,说f = f(x)
I have a list of values of x. 我有一个x值列表。 q is just the data list
q只是数据列表
I wish to create a new list with values of f'(x) for all x values I have. 我希望为我拥有的所有x值创建一个值为f'(x)的新列表。
f = sqrt(x)
xt = ts(q)
count = length(xt)
f' = rep(0,count)
for (k in 2:count){
f'[k] = D(f,"x")[k]
}
This isn't working. 这不起作用。 Could someone please help?
有人可以帮忙吗?
you can do this 你可以这样做
d<-D(substitute(sqrt(x)),"x")
x<-1:5 #if u have a list use unlist example x<-list(1,2,3) x<-unlist(x)
eval(d)
The trick is that you have to pass an expression, if you do something like 诀窍是,如果您执行以下操作,则必须传递一个表达式
f=sqrt(x), R will compute the value of sqrt(x) and if you don't define x (and in any case is not what u want). f = sqrt(x),R将计算sqrt(x)的值,如果您未定义x(无论如何都不是您想要的),R会计算。 You have to pass an expression and substitute just don't evaluate.
您必须传递一个表达式并替换为不求值。 You want to eval after the derivative is computed.
您要在计算导数后进行评估。
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