could you give me advice?

[jlee-2]

mu=0.2, 0.25, ..1

tw(mu)>>> this mean is that tw(0.2)=19.54, tw(0.25)=15.86.....

and "c" is also including mu.

it means c(mu). c(0.2)=689.23, c(0.25)=662.54....

I want to express like upper.

Is it possible?

[RichardJ]

Use a spline to convert the table columns to a function. If columns 1 and 2 are vectors (not range variables!),

coeffs:=cspline(col1,col2)

tw(mu):=cspline(coeffs,col1,col2,mu)

[jlee-2]

thank you~ I will try to do it

[Fred_Kohlhepp]

Richard has shown you spline fitting to create functions that fit datapoints represented by vectors.

There are many others.

Splines will pass thru the data points exactly, but they may fluctuate wildly between the points. Other operators assume a function type and do least square fitting to find the parameter values for closest fit. Attached is a sheet demonstrating a fourth order polynomial fit for your twist data. Note that it is not exact!

For many applications you may want to do straight line interpolation between points; research "linterp" for that application.

[jlee-2]

thank you^^