Re: [R] error propagation - hope it is correct subject

2003-12-23 Thread Thomas W Blackwell
Petr - Yes, you are interpreting the second suggestion exactly correctly, apart from concern for possible correlations among x1,x2,x3. If one can treat them as independent, I would do exactly as you show: generate a vector of, say, n = 1 simulated draws from x1, another vector of the same le

Re: [R] error propagation - hope it is correct subject

2003-12-23 Thread Petr Pikal
Hallo Thomas Thank you for your answer, even I am not sure how to do it in R (or maybe at all). My mathematics background is only faint so I drop the first possibility which is for me rather cryptic. Does your second suggestion mean: 1: compute random variable y <- f(rnorm(n,mymeanx1,my

Re: [R] error propagation - hope it is correct subject

2003-12-22 Thread Thomas W Blackwell
Petr - Very briefly, I think of three ways to approximate the standard deviation of y = f(x1,x2,x3). (1) linearise f() and use the covariance matrix of [x1,x2,x3]. (2) simulate draws from the joint distribution of [x1,x2,x3], then compute the sample std dev of resulting f()s. (3)

[R] error propagation - hope it is correct subject

2003-12-22 Thread Petr Pikal
Dear all Please, can you advice me how to compute an error, standard deviation or another measure of variability of computed value. I would like to do something like: var(y) = some.function(var(x1),var(x2),var(x3)) for level F1 (2,3,...) Let say I have some variables - x1, x2, x3 (two compute