# [R] Error with constrained curve fitting through specific points

Tung Nguyen th@nhtungm||@n @end|ng |rom gm@||@com
Wed Jan 22 16:00:39 CET 2020

```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

[[alternative HTML version deleted]]

```

More information about the R-help mailing list