FIT-COMPOSITE-BASELINE

Fits a combination of a polynomial and set of harmonic sinusoids to the current spectrum, within the nominated x-axis intervals (10 intervals max). Invented for analysis of baseline ripple data from Parkes, and still the only routine for analysing sinusoidal baselines (apart from Fourier analysis).

The problem is non-linear if the sinusoid period is undetermined -- you can allow this to be fitted or not as you require.

If the fit is successful the stack is pushed and the resulting baseline is written to the current spectrum. Just use SUBTRACT-SPECTRUM to calculate the residuals.

Relevant flags:

N_POLY

I4

Number of polynomial coefficients.

POLY_COEFF(30)

R4

Polynomial coefficients.

N_SIN

I4

Number of harmonics to fit.

AMP_PHASE(28)

R4

Amplitude and phase of sinusoidal components.

FREQ_COEFF

R4

Fitted frequency (may be negative if constrained to be constant).

N_INTS

I4

Number of intervals to use for analysis.

BLF_INTS

R4

Pairs of channels defining spectral intervals to be used for baseline fitting, analysis etc..

FIT_TOL

I4

Specifies the convergence criterion. If the fractional change in the sum-squared-error from one interation to the next is less than FIT_TOL then the process has converged. [.05]

MAX_ITS

I4

Specifies the maximum number of iterations to be executed. [20]

FIT_DEBUG

I4

Determines the type and amount of debug information written to the screen.

-1	no printing [Default]
0	printing after convergence only
1	print diagnostic information
2	as above plus gradient check

Examples:

    >> fit-composite-baseline<CR>
    Type intervals, one at a time, CTRL(Z) to finish
    Current units are km/s  

    # -10 10<CR>
    # ^z<CR>

    Estimate of polynomial coefficients for x**n
    One at a time, CTRL(Z) to finish

    Current units are km/s  

    # (x** 0) 0.2<CR>
    # (x** 1) ^z<CR>

    Estimate of fundamental period,-ve if const;CTRL(z)=none [  0.0000] 5.0<CR>

    Estimates of Amplitude and phase for each harmonic
    Term at a time, CTRL(Z) to finish

    Current units are km/s  

    # 1 0<CR>
    # ^z<CR>


         No of Iterations =     7          Final SUMSQ = 0.9940E+01

                  Parameters of Least-Square Baseline
                Polynomial terms - Coefficients of X**n
                           0      0.36
                  Fundamental period is  25.2 km/s  
                  Harmonic  Amplitude    Phase(km/s  )
                       1       0.92         13.04



    Baseline calculated - Pushed into stack
    ..