#carica e scarca condensatore
# GdA, giugno 06
 
c <- 100E-9
r <- 10000
v0 <- 1
 
tau <- r*c
t <- seq(0, 6*tau, length=100)
v.c <- v0*(1-exp(-t/tau))
v.sc <- v0*exp(-t/tau)
plot(t, v.c, type='l')
 
plot(t, v.sc, type='l')
plot(t, v.sc, type='l', log='y')
plot(t, v0-v.c, type='l', log='y')
 
lm(formula = log(v.sc) ~ t)
fit <- lm (log(v.sc) ~ t)
str(fit)   # info s come e' fatto l'oggetto fit
fit$coefficients
fit$coefficients["t"]
tau.m <- -1/fit$coefficients["t"]
 
v <- numeric()
for (i in 1:length(t)) v[i] <- v.sc[i] + rnorm(1, 0, v.sc[i]*0.05)
fit <- lm (log(v) ~ t)
fit$coefficients
tau.m <- -1/fit$coefficients["t"]
tau.m
summary(fit)
vcov(fit)
sqrt(vcov(fit)[2,2]) 
 
# alteratva :
summary(fit)$cov.unscaled
# vedi, ancora:
s.fit <- summary(fit)
tr(s.fit)