rfmig_cboot.f -- code to compute harmonic expansion of RFs with back-azimuth

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c code computes frequency-domain stacks of receiver functions that follow a harmonic expansion in baz
c for both radial and transverse RFs there are constant terms and sin/cos terms for 2- and 4-lobed
c amplitude dependence. The constant term should be zero for the transverse RF.
c The 2-lobed terms govern dipping interface effects and tilted symmetry-axis ansotropy.
c The 4-lobed term is anisotropy with a horizontal axis
c The code regresses for the harmonic expansion, and bootstrap-resamples the data to estimate the
c uncertainty of the harmonic terms.
c
c output files are out[rt]_cexp.grid -- harmonic-expansions of the RFs, in time domain
c out[rt]1_cexp.grid -- harmonic-expansion RFs plus bootstrap uncertainty
c out[rt]2_cexp.grid -- harmonic-expansion RFs minus bootstrap uncertainty
c out[rt]_bbaz.grid -- harmonic-expansion RFs computed for ordered baz values
c
c migrates MTC receiver functions in the frequency domain.
c requires a stacking model in the anirec format
c such a model may have anisotropy parameters,
c but migration code only uses the isotropic velocities.

c the output of this program is a least-square regression of RFs in the freq
c domain, with complex-valued coefficients for the
c constant, cos(baz)R+sin(baz)T, cos(baz)R-sin(baz)T,
c cos(2*baz)R+sin(2*baz)T, cos(2*baz)R-sin(2*baz)T variations