Sign Changes

Count the number of times the first, or second, derivative of a spline changes sign.

Usage

sign_changes(
  object,
  lower = min(object$bknots),
  upper = max(object$bknots),
  n = 1000,
  derivative = 1L,
  ...
)

Arguments

object

a cpr_cp object

lower

the lower limit of the integral

upper

the upper limit of the integral

n

number of values to assess the derivative between lower and upper.

derivative

integer value denoted first or second derivative

...

pass through

Value

the number of times the sign of the first or second derivative changes within the specified interval.

See also

wiggle

Examples

xvec <- seq(0, 6, length = 500)

# Define the basis matrix
bmat1 <- bsplines(x = xvec, iknots = c(1, 1.5, 2.3, 4, 4.5))
#> Warning: At least one x value >= max(bknots)
bmat2 <- bsplines(x = xvec)
#> Warning: At least one x value >= max(bknots)

# Define the control vertices ordinates
theta1 <- c(1, 0, 3.5, 4.2, 3.7, -0.5, -0.7, 2, 1.5)
theta2 <- c(1, 3.4, -2, 1.7)

# build the two control polygons
cp1 <- cp(bmat1, theta1)
cp2 <- cp(bmat2, theta2)
plot(cp1, cp2, show_cp = FALSE, show_spline = TRUE)


sign_changes(cp1)
#> [1] 4
sign_changes(cp2)
#> [1] 2