Get coordinates of points generated by spline curve

Hello everyone,

Because I need to use a curve which is from a book, so I'm trying to plot this curve on matlab in order to use it after that.

Indeed, with coordinates of some points I know, I've succeeded to plot the curve with spline function.

The problem is that I need now to recover some points of the curve which weren't defined at the beginning for the plot. Can I do that?

I've tried with:

yMin = min(y); yMax = max(y); ylim([0 yMax]); yMin = min(y) indexAtMin = find(y == yMin); xAtMin = x(indexAtMin)

But this works only with points defined before!

Thank you for your answer.