[R] Fitting problem

[pj-uk]

#### Updated!

#### 

"MH"<-function(field,diameter,mu=10e-7,sig=0.1,Ms=100,chi=0){ 
#variables mu, sig, chi, Ms 
#input: field and diameter 
#all in CGS 
rho <- 5 
kb <- 1.38e-16 
t <- 300 
length.d<-length(diameter) 
length.H<-length(field) 
M<-double(length.H) 
for (i in 1:length.H){ 
        S1<-0 
        S2<-0 
        H <- field[i] 
        for (j in 1:length.d){ 
                d<-diameter[j] 
                vol <- 4/3*pi*(d/2)^3 
                lognorm <-
1/(d*sig*sqrt(2*pi))*exp(-(log(d)-log(mu))^2/(2*sig^2)) 
                lang <- 1/tanh(Ms*rho*vol*H/(kb*t))-1/(Ms*rho*vol*H/(kb*t)) 
                S1 <- S1 + lognorm*vol*lang 
                S2 <- S2 + lognorm*vol	
        } 
        M[i] <- Ms*S1/S2 + chi*H	
} 
M 
} 

###

htest<- (-10:10)*200 
dtest<- (5:15)*1e-7 
mtest<- MH(field=htest,diameter=dtest) + rnorm(21)  ##also added some
noise!! 
df <- data.frame(H=htest,M=mtest) 

fit <- nls(M~MH(H,(5:15)*1e-7,mu,sig,Ms,chi),data=df,start=list(mu=10e-7,
sig=0.1, chi=0, Ms=100)) 

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