How to do logrithmic interpolation like Labview Graph?

[avater]

Hi

I have a question about  interpolation logrithmically.For example I have a line which has only 2 points

(584,7.21)

(14137,0.08)

so when you show this it on the graph,you'll have a straight line on it.But with different Y mapping,the point indide this line is totoally different.

See pics below.

Inside this line,I sample a point at X=6000,but get a totally different Y, they are about 1.2 and 4.3.

Value 4.3 can be get easily by the vi "Interpolation 1D array" ,which is a linear interpolation.

But how to get the value 1.2 ? Thus how to interpolate a array logrithmically?

How does Labview graph calculate this? or Is there a way to get the data from the graph,although there is actually no data at X=6000.

Appreciate your opinion on this.Thanks.

[IanSh · Accepted solution]

You can put the Y values through a log function before you interpolate, then 10^x the resulting Y value. I'm not aware of a native logarithmic interpolation.

[avater]

It works.

Thanks very much.