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c++ cubic spline library

License: GNU General Public License v2.0

C++ 100.00%

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spline's Issues

Can implement a 'not-a-knot' boundary condition like Python?

I found that the default result is the same as Python(scipy.interpolate.CubicSpline)'s natural boundary condition.
But I don't know how to match the default result of Python(with default boundary condition not-a-knot)

.Solve(-) not working, gives out empty vector

Hi, great work on the splines code. I just have a small issue i stumbled upon using it in my project. I'm trying to recreate this splines into my code. Thanks in advance! Here is the issue, the splines and my code:

 int WorldGen(float Cont, float Eros, float PV ) {
			int worldHeight = 0;
			//Peakes & Valleys
			std::vector<double> x1, y1;
			x1.push_back(0.05f);
			y1.push_back(0.f);

			x1.push_back(0.1f);
			y1.push_back(0.1f);

			x1.push_back(0.325f);
			y1.push_back(0.2f);

			x1.push_back(0.5f);
			y1.push_back(0.21f);

			x1.push_back(0.65f);
			y1.push_back(0.55f);

			x1.push_back(0.9f);
			y1.push_back(0.61f);

			x1.push_back(1.f);
			y1.push_back(0.65f);
			tk::spline PVSpl;
			PVSpl.set_points(x1, y1);

			//Erosion
			std::vector<double> x2, y2;
			x2.push_back(0);
			y2.push_back(1);

			x2.push_back(0.15f);
			y2.push_back(0.55f);

			x2.push_back(0.3f);
			y2.push_back(0.41f);

			x2.push_back(0.32f);
			y2.push_back(0.45f);

			x2.push_back(0.45f);
			y2.push_back(PVSpl.solve(PV)[0]);

			x2.push_back(0.6f);
			y2.push_back(0.11f);

			x2.push_back(0.7f);
			y2.push_back(0.11f);

			x2.push_back(0.72f);
			y2.push_back(0.28f);

			x2.push_back(0.78f);
			y2.push_back(0.28f);

			x2.push_back(0.79f);
			y2.push_back(0.11f);

			x2.push_back(0.85f);
			y2.push_back(0.05f);

			x2.push_back(1.f);
			y2.push_back(0.05f);
			tk::spline ErosSpl;
			ErosSpl.set_points(x2, y2);

			//Continetalness
			std::vector<double> x3, y3;
			x3.push_back(0);
			y3.push_back(1);

			x3.push_back(0.09f);
			y3.push_back(0.025f);
			
			x3.push_back(0.345f);
			y3.push_back(0.025f);
			
			x3.push_back(0.385f);
			y3.push_back(0.435f);

			x3.push_back(0.515f);
			y3.push_back(0.435f);

			x3.push_back(0.525f);
			y3.push_back(0.9f);

			x3.push_back(0.55f);
			y3.push_back(0.915f);

			x3.push_back(0.72f);
			y3.push_back(ErosSpl.solve(Eros)[0]);

			x3.push_back(1.f);
			y3.push_back(0.98f);

			tk::spline ContSpl;
			ContSpl.set_points(x3, y3);
			
			worldHeight = ContSpl.solve(Cont)[0] * 100;

			return worldHeight;
		}

How to do a spline and divide the spline into points of equal distance?

So task like the following:
4 points input
100 points output in between the first and the last one

Compile error

When running make in the examples folder I get:

g++ -I../../alglib/src -I../src -O2 -DNDEBUG -Wall -c interpol_alglib.cpp -o interpol_alglib.o
interpol_alglib.cpp:4:37: fatal error: interpolation.h: No such file or directory
 #include "interpolation.h" // alglib

Looks like there is a missing file from alglib - perhaps document this better?

x need to increase monotonically

I use this to smooth the path, but the x of the path point is not necessarily monotonically increasing. How should I deal with it?

typo

Hi,

very nice code. Looks like you have a typo for case 2 below. Shouldn't it be 2.0*m_b0 instead of 2.0*m_b0*h?

if(x<m_x[0]) {
        // extrapolation to the left
        switch(order) {
        case 1:
            interpol=2.0*m_b0*h + m_c0;
            break;
        case 2:
            interpol=2.0*m_b0*h;
            break;
        default:
            interpol=0.0;
            break;
        }

warning: ‘CLASS’ has a field ‘CLASS::spline_’ whose type uses the anonymous namespace

Usage of spline as a member of class creates warning.

#include "spline/spline.h"
class CLASS {
tk::spline spline_;
}

first derivative

Is anyone adding functionality to calculate the first derivative at the interior points?

Is it a Cubic B-Spline Function?

I ran the code twice with 5 control points, in the second run I changed the fourth control point by a certain magnitude and observed that the global shape of the spline changed completely. I was hoping for more local control.

Computation time

Hello. Thank you for this library. It is quite easy to use.
Your benchmarks shows that it takes 0.2sec to access spline 10^7 times.
But it takes 100 seconds in my case. I build a spline and include it as a member to my class.
Then in another method I access this spline about 10^7 times.
Please suggest an algorithm optimization.

Is this should be h^2 for first_deriv?

spline/src/spline.h

Line 539 in 5894bea

interpol=(3.0*m_d[idx]*h + 2.0*m_c[idx])*h + m_b[idx];

Is this should be h^2 for first_deriv?
interpol = (3.0 * m_d[idx] * h * h + 2.0 * m_c[idx]) * h + m_b[idx];

[question] Interpolating closed spline ?

Hello,

Is this library able to interpolate a closed spline curve ?

Thanks

Not-a-knot index error

Hi @ttk592,

I think this line is wrong: https://github.com/ttk592/spline/blob/master/src/spline.h#L332

Shouldn't it be: rhs[n-1] = 0.0;?

More liberal license?

May I suggest a change to a more liberal license (MIT, LGPL, Apache2...)? I see it more appropriate for the scope and the amount of code. Of course it's your choice.

How to obtain the curve length of a spline

I need to find the curve length , could you please give me some suggestoins.