[R] nls, predict() problem

[Kay Cichini]

hello,

can anyone help with this:

###########################################################
###data: measurments (response = trans) run several times at the same
predictor value level (press)

por<-data.frame(list(structure(list(run = structure(c(1L, 1L, 1L, 1L, 2L,
2L, 
2L, 2L, 3L, 3L, 3L, 3L), .Label = c("1", "3", "4"), class = "factor"), 
    press = c(15, 21, 24, 29.5, 15, 21, 24, 29.5, 15, 21, 24, 
    29.5), tr_rel = c(1, 0.459454191, 0.234697856, 0.135282651, 
    1, 0.853283066, 0.306314797, 0.186302231, 1, 0.42980063, 
    0.103882476, 0.086463799), tr = c(513, 235.7, 120.4, 69.4, 
    318.3, 271.6, 97.5, 59.3, 476.5, 204.8, 49.5, 41.2)), .Names = c("run", 
"press", "tr_rel", "tr"), row.names = c(NA, -12L), class = "data.frame")))
attach(por)

###nls:

summary(mod1<-nls(tr ~ SSlogis( log(press), Asym, xmid, scal)))

press_x <- seq(15, 30, length = 100)

####predict() somehow doesn't recognize the list and returns values 
####as if list argument was absent:

predict(mod1,list(Pressure=press_x))

####consequently plotting of fitted line doesn't work either:

plot(press,tr)
lines(press_x,predict(mod1,list(pressure=press_x)))
###########################################################


thanks a lot in advance for any hints - 

greetings,
kay
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