[R] Error with constrained curve fitting through specific points

[Rui Barradas]

Hello,

This seems to "work". It doesn't give errors nor warnings and the fitted 
line passes through the given points.


fit_result <- cobs(dat$x, dat$y,
                    constraint = "increase",
                    lambda = 0.1,
                    pointwise = con)

plot(y~x, dat)
pred <- predict(fit_result)
lines(pred[,1], pred[,2], col = "red")


Hope this helps,

Rui Barradas

Às 15:00 de 22/01/20, Tung Nguyen escreveu:
> Hello R-Help,
> 
> I'm trying to find the best fitting curve through a given set of points.
> The fitted curve must also pass through these points. I found an answer on
> Cross Validated which suggested to use the `cobs: Constrained B-Splines
> (Sparse Matrix Based)` package. However, I got an error while testing it
> with my sample data:
> 
> Error in x %*% coefficients: NA/NaN/Inf in foreign function call (arg 2)
> 
> *My question*: what caused this error and how can I fix it? Any suggestion
> is greatly appreciated. Thanks!
> 
> library(cobs)
> 
> dat <- data.frame(
>    x = c(1e-06,0.25,0.5,0.75,1,2,3,4,5,6),
>    y = c(1e-07,1.925,2.9625,3.469375,
>          3.875,4.5315,4.89,5.09375,5.216,5.46))
> dat
> #>          x         y#> 1  1.0e-06 0.0000001#> 2  2.5e-01
> 1.9250000#> 3  5.0e-01 2.9625000#> 4  7.5e-01 3.4693750#> 5  1.0e+00
> 3.8750000#> 6  2.0e+00 4.5315000#> 7  3.0e+00 4.8900000#> 8  4.0e+00
> 5.0937500#> 9  5.0e+00 5.2160000#> 10 6.0e+00 5.4600000
> # visual inspection
> plot(dat); lines(dat)
> 
> # define constrained points
> con <- matrix(
>    cbind(c(0,0,0,0,0,0,0,0,0,0),
>          c(1e-06,0.25,0.5,0.75,1,2,3, 4,5,6),
>          c(1e-07,1.925,2.9625,3.469375,
>            3.875,4.5315,4.89,5.09375,5.216, 5.46)),
>    ncol = 3, nrow = 10)
> # curve fitting
> fit_result <- cobs(dat$x, dat$y, pointwise = con)*#> qbsks2():
> #>  Performing general knot selection ...
> #> Error in x %*% coefficients: NA/NaN/Inf in foreign function call (arg 2)*
> 
> 
> Best regards,
> 
> -- Tung
> 
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> 
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