Problem: to find 1st and 2nd derivatives of a circular spline

Problem: to find 1st and 2nd derivatives of a circular spline in
order to calulate the radius of curvature of the various points
around a circle.

This is for my MSc dissertation. I am calulating the max strain in a
pipeline section which has a dent. Part of the calculation requires
the radius of curvature of the pipe wall to be cacluated in the cross
sectional plane.

I have constructed a spline which interpolates the profie of the
dented pipe through the cross section using the spline command
(pp-form), the spline is constucted using an array of the x,y points
aganst 2xPi. I now need to to calculate the 1st and 2nd derivatices
of the spline. Unfortunatley when using the fnder command it gives
the derivatives as an x,y array - I need one value for each
derivative.

Can anyone point me in the right direction

Thanks
.

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