# mtmAR: Intermediate spectrum test of Thomson et al. (2001) In astrochron: A Computational Tool for Astrochronology

## Description

Perform the 'intermediate spectrum test' of Thomson et al. (2001).

Paraphrased from Thomson et al. (2001): Form an intermediate spectrum by dividing MTM by AR estimate. Choose an order P for a predictor. A variety of formal methods are available in the literature, but practically, one keeps increasing P (the order) until the range of the intermediate spectrum Si(f) (equation (C4) of Thomson et al., 2001) stops decreasing rapidly as a function of P. If the intermediate spectrum is not roughly white, as judged by the minima, the value of P should be increased.

## Usage

 ```1 2``` ```mtmAR(dat,tbw=3,ntap=NULL,order=1,method="mle",CItype=1,padfac=5,demean=T,detrend=F, output=1,xmin=0,xmax=Nyq,pl=1,genplot=T,verbose=T) ```

## Arguments

 `dat` Stratigraphic series for analysis. First column should be location (e.g., depth), second column should be data value. `tbw` MTM time-bandwidth product. `ntap` Number of DPSS tapers to use. By default, this is set to (2*tbw)-1. `order` Order of the AR spectrum. `method` AR method ("yule-walker", "burg", "ols", "mle", "yw") `CItype` Illustrate (1) one-sided or (2) two-sided confidence intervals on plots `padfac` Pad with zeros to (padfac*npts) points, where npts is the original number of data points. `demean` Remove mean from data series? (T or F) `detrend` Remove linear trend from data series? (T or F) `output` Output (1) intermediate spectrum and confidence levels, (2) intermediate spectrum, (3) confidence levels `xmin` Smallest frequency for plotting. `xmax` Largest frequency for plotting. `pl` Plot logarithm of spectral power (1) or linear spectral power (2)? `genplot` Generate summary plots? (T or F) `verbose` Verbose output? (T or F)

## References

Thomson, D. J., L. J. Lanzerotti, and C. G. Maclennan, 2001, The interplanetary magnetic field: Statistical properties and discrete modes, J. Geophys.Res., 106, 15,941-15,962, doi:10.1029/2000JA000113.

`eha`, `lowspec`, `mtm`, `mtmML96`, `periodogram`, and `spec.mtm`
 ``` 1 2 3 4 5 6 7 8 9 10``` ```# generate example series with periods of 400 ka, 100 ka, 40 ka and 20 ka ex = cycles(freqs=c(1/400,1/100,1/40,1/20),start=1,end=1000,dt=5) # add AR1 noise noise = ar1(npts=200,dt=5,sd=.5) ex[2] = ex[2] + noise[2] # MTM spectral analysis, with conventional AR1 noise test pl(1,title="mtmAR") mtmAR(ex) ```