splev

Syntax

splev(x, tck)

Arguments

x is a vector that specifies a set of data points to obtain corresponding values on the spline.

tck can be a tuple of length 3 or a B-spline curve object that contains a vector t of knots, the B-spline coefficients, and the degree k of the spline. It can be generated with function splrep. Note that the spline degree k must satisfy 1 <= k <= 5.

Details

splev, short for Spline Evaluation, is used to evaluate B-spline curves or their derivatives. Given the knots and coefficients of the B-spline representation, this function calculates the values of the smooth polynomials and their derivatives. If NULL is included in the input values of x or tck, it will be filled with 0.

Return value: y, a DOUBLE type vector that represents the array of spline function values evaluated at points x.

Examples

x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
y = [0, 3, 5, 6, 5, 3, 1, 2, 4, 5]
newx = [0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5]
t=[1,3,5,8]
tck= splrep(x, y, t=t)
print(tck)
// output
([0,0,0,0,1,3,5,8,9,9,9,9],[0,2.234794827972243,2.999908797063527,8.195517483732592,0.982766102937427,0.416533320193195,6.868465914739519,5,0,0,0,0],3)

newy = splev(newx, tck)
print(newy)
// output
[2.147514374187927,3.928180605155257,5.780093403045226,5.788551610920491,3.842319632145274,1.928386784305488,1.343262026468735,2.600266282317609,5.680148059970901,-0.902321655035049]