Interpolation of a set of x , y data to a curve

I want to interpolate a set of data which are x , y points of a hystersis plot.

please help me how can I find best interpolation in such case and after that how can I find it's slope to find knee point?

thanks!

Answer 1

[Image Analyst]

Start by running my spline demo. Adapt as needed.

[saeid haghighipour]

thanks!

As IEC standard I should find a point on interpolated curve which resolve this situation:

if X present value preseeds 1.5 times of it's previous value , the Y new value of this point preceeds 1.1 times of previous value.

do you know how can I find such point on this curve?

[Image Analyst]

Did you mean Y instead of X? I'm thinking so. If so, try this:

indexes = Y(2:end) > 1.5 * Y(1:end-1);
Y(indexes) = 1.1 * Y(indexes - 1);

If you really meant what you said, then replace Y by X in the first equation:

indexes = X(2:end) > 1.5 * X(1:end-1);
Y(indexes) = 1.1 * Y(indexes - 1);