hey,

Anyway to get excel to interpolate?

 

Here it is....x data is in row 1, y data is in row 2 to it looks like this (start in column A)

x1 x2 ?
y1 y2 y

This will solve for the question mark in x.

=+A1+ (C2-A2)/(B2-A2)*(B1-A1)

or the other case, this will solve for the question mark in y.

x1 x2 x
y1 y2 ?

=+A2+ (C1-A1)/(B1-A1)*(B2-A2)

 

man i've tried hard to understand what you posted and i just don't get it.

Sorry, i think i'm pretty experenced with excel too.. You think you could go into a little more detail.

Pardon my ignorance

 

It helps to think about what interpolation actually is. You only need two points in order to calculate the corresponding number for any third point you want to come up with. He had you set up your data in rows A and B. Your known "x" values are in A1 and B1, your known "y" values in A2 and B2.

If you have a third y value and need to find x:
Put the y value in C1
Put the first equation he wrote in C2

If you have a third x value and need to find y:
Put the x value in C2
Put the second equation he wrote in C1

Did that help any?

 

Good explanation, but I believe that you mixed it up a little. It should read

If you have a third y value and need to find x:
Put the y value in C2
Put the first equation he wrote in C1

If you have a third x value and need to find y:
Put the x value in C1
Put the second equation he wrote in C2


And expanding more on the topic


Say I have a have 500 hp Camaro that will run an 11.0 in the 1/4 mile. My friend has a 350 hp Camaro that runs 14.5 in the 1/4 mile. A third friend runs 13.0 in the 1/4 mile but doesn't know his horsepower.

With interpolation in excel, put the following

In A1, put 11.0
In B1, put 14.5
In C1, put 13.0

In A2, put 500
In B2, put 350
In C2, put =+A2+ (C1-A1)/(B1-A1)*(B2-A2)

In C2, the interpolate value will be determined by the equation in C2.

 

Alvin,

Another real easy way is to use the SLOPE and INTERCEPT functions.

I've attached a spreadsheet as an example. This method lets you interpolate and/or extrapolate.

Note that the file attachment has a '*.bmp' extension, but that's not it. Once you download, rename the extension to '*.XLS'. Apparently we're not able to upload non-picture files right now as direct attachments.

Excel has LOTS of power. This isn't even a surface scratch.

Hope this helps.
-Craig

 

Ah, I see now.. that makes a bit more sence.

Hey do you guys know how to do good datasmoothing? The reason why I ask is because alot of times when I tune with BLMS you won't touch on areas like 900RPM 100KPA because the car obviously doesn't go there often.

I tuned a fast system for someone once and I liked a feature they had where you could highlight some cells push a button and it would do nice smoothing over it.

This would be cool cause if the car would venture into these areas days or years after tuning is finished the VE values would be more reasonable and hopefully you wouldn't feel it or notice it.

 

Wanting to 'smooth out those lines' eh?

You can do something like that pretty easy, also with Excel. Interpolation is along the right lines (no pun intended), but I guess you're looking for a 'soft' interpolation. Maybe someday we won't even have to LOOK at the data, and the tools can just do it all for us. ;^).

You can do two-dimensional extrapolation as well. Same thing as what we just talked about, except you have x(RPM), y(MAP), and z(VE). So you can come at the 'empty' cell from two angles, one along the RPM axis and the other along the MAP axis. Then do the net determination of the two coincident slopes.

Maybe not what you're looking for, but some spouting off nonetheless...