Piecewise polynomial integration (ppint)

Is the command piecewise polynomial integration (ppint) not working anymore? Below is an example given by an old member of the community https://de.mathworks.com/matlabcentral/fileexchange/13812-splinefit?focused=7896654&tab=function:

x = linspace(-pi,pi,7);
y = sin(x);
plot(x,y) 
hold on
pp = interp1(x,y,x,'spline');
plot(x,pp+0.1)
I = ppint(pp,1)

'Undefined function or variable' error comes up. If it is not available anymore, what is the alternative for such a case?

Answer 1

[John D'Errico]

Just use fnint.

x = linspace(0,2*pi,20);
y = sin(x);
pp = spline(x,y);
ppcos = fnint(pp);
fnplt(ppcos)

As you can see, we get effectively -cos(x). Of course, the constant of integration is missing.

[Jamal Nasir]

Thank you for your answer. Unfortunately, our matlab license doesn't include that functionality. We need to change that. Could you please, anyways, also tell me the double integration function? I actually need to fit ESR/EPR data and then double integrate to quantify the electron spins.

[John D'Errico]

I think fnint comes with the curvefitting toolbox. The curve fitting toolbox is well worth obtaining.

If you had fnint, then the double integral would be just

fnint(pp,2)

I could write a ppint code, but it looks like Walter has already offered a source.

Answer 2

[Walter Roberson]

ppint has never been part of MATLAB. See https://ww2.mathworks.cn/matlabcentral/fileexchange/13812-splinefit