## "too many points" error - FFT

## "too many points" error - FFT

(OP)

I have a rather large (110K points) set of acceleration data that I must analyze in Mathcad Plus 6.0. I have managed everything up to plotting the FFT data in frequency domain. I can plot with a simple n=1..32768 for the x axis, but if I try to use the frequency data (n=.004,.008..128) for the x-axis I get a "too many points" error.

Any thoughts? Is .004 just too small to be on a log-scale x-axis?

Thanks in advance for the help!

Note: numbers rounded to protect the significant

Any thoughts? Is .004 just too small to be on a log-scale x-axis?

Thanks in advance for the help!

Note: numbers rounded to protect the significant

## RE: "too many points" error - FFT

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

## RE: "too many points" error - FFT

I set up a new variable d := log(.004), log(.008)..log(128) and attempted to plot with d on the x-axis. I had no success plotting (on a standard scale); same "too many points" error.

Any other suggestions?

## RE: "too many points" error - FFT

## RE: "too many points" error - FFT

I'm confused on how "log(.004),log(.008)...log(128) is only 7 steps." I get -2.398, -2.097, -1.796... 2.107.

## RE: "too many points" error - FFT

I divided by the wrong number - should be 16 steps.

## RE: "too many points" error - FFT

Another approach is to just plot two vectors. I got in the habit of doing that when I used Axum for my plots. In this case you would use your range variable (n) to make a vector with you FFT amplitude, and one with your frequency (for instance: frequency[n-1 := n/256 (assuming ORIGIN=0)). Then you could plot those two vectors (no subscripts).

Peter

## RE: "too many points" error - FFT

I used the n/256 on the x-axis for now, but will look into using vectors in the future.

Now if I could just smooth the plots I'd be all set... but that's a new thread if I can't figure it out.

## RE: "too many points" error - FFT

TTFN