[R] Error with constrained curve fitting through specific points

[Tung Nguyen]

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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