Zero149 - 6 months ago 29

R Question

There was a problem in constructing the approximation of the diode voltage-ampere characteristic(code below).

`library("ggplot2")`

mat <- read.table(file='vah_p_1',header =TRUE)

chart <- ggplot() + geom_point(data = mat,aes(x = x, y = y)) +

stat_smooth(method = 'nls', formula = 'y~a*(exp(x/b) - 1)',

method.args = list(start=c(a=0.1646, b=9.5e-8)),se=FALSE)

chart

The

`x y`

0 4

0.25 5

0.27 6

0.29 7

0.31 8

0.33 10

0.34 13

0.36 16

0.37 20

0.38 23

0.39 28

0.4 37

0.41 43

0.42 55

0.43 67

0.44 81

0.45 94

0.46 118

0.47 143

0.48 187

0.49 225

0.5 272

0.51 340

0.52 430

0.53 510

0.54 626

0.55 900

0.56 1020

0.57 1220

0.58 1640

0.59 1850

0.6 2360

0.61 2930

0.62 3570

0.63 4290

0.64 5000

0.65 6570

0.66 7390

0.67 9230

0.68 9960

Approximation line is not being built !!! What is the problem? How to find the approximation error?

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Answer Source

Good evening :)

I usually put the `aes`

and `data`

in to the initial ggplot for these cases. When I did that, it threw a warning. I tried the `nls`

stand alone and there is an error in there. I'd suggest investigating this, and see if resolving the problem resolves your plot issues. Code:

```
chart <- ggplot(data = mat, aes(x = x, y = y)) + geom_point() +
stat_smooth(method = 'nls', formula = 'y~a*(exp(x/b) - 1)',
method.args = list(start=c(a=0.1646, b=9.5e-8)),se=FALSE)
chart
nls('y~a*(exp(x/b) - 1)', mat, start=c(a=0.1646, b=9.5e-8))
```

Error thrown is:

```
Error in numericDeriv(form[[3L]], names(ind), env) :
Missing value or an infinity produced when evaluating the model
```

Edit: Always check your starting points:

```
a=0.1646
b=9.5e-8
y <- a*(exp(mat$x/b) - 1)
y
plot(mat$x, y)
```

Transformation produces almost all infinites

I followed this link for style: https://plot.ly/ggplot2/stat_smooth/

Cheers, Jonny

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