mtmAR {astrochron} | R Documentation |

## Intermediate spectrum test of Thomson et al. (2001)

### 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

```
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.

### See Also

`eha`

, `lowspec`

, `mtm`

, `mtmML96`

, `periodogram`

, and `spec.mtm`

### Examples

```
# 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)
```

*astrochron*version 1.3 Index]