I am fitting a 2D depth surface (z_mod) to some 170 data points (z_obs) using greenspline. To account for noise in the data, I’m using singular value decomposition to model the surface and am currently choosing a eigenvalue cut-off subjectively, using: gmt greenspline $dep -G$svd -L $R -Z2 -I$I -W …

Dear community I could compile the greenspline source without major issues and now have my private version in which I write out the model norm as an INFORMATION. for (e = 0; e < (uint64_t)n_use; e++) { /* Only loop over the first n_use eigenvalues (if restricted) */ GMT_Report (API, GMT_M…

@pwessel : Is it worth implementing into gmt with an extra option now that @wsja has basically done it?

Looking at this, could your modnorm value be added as a column to the output file that -E sets? Would be pretty simple for me to add that, possibly via a -E modifier.

But first, why were you unable to use -C+f? Append +f file to save the eigenvalues to the specified file for further analysis

The eigenvalues is not what I need, I need the alphas, dependent on n_use. From C+f I get what I think would be what be the singular values (The diagonal elements of S, from G = USV^T; they are in the 1e18 - 1e0 range. I would expect the alphas to span at most 5 or 6 orders of magnitude). Moreover…

OK, got you this time. Let me see if I can whip out a branch for your testing,

[image] wsja: modnorm += *obs * *obs; I dont know what you mean here. obs is an array.

OK, that is what I did. See if you can test this branch and comment on what is missing: https://github.com/GenericMappingTools/gmt/pull/7358

I think there is some syntactical mishap: Should it be: -E+nfile (this throws an: [Session greenspline (0)]: Error returned from GMT API: GMT_ERROR_ON_FOPEN (15)) or -Efile+n (which does not recognize the +n flag, but simply appends an “+n” to the file name)

Syntax is -E[misfitfile][+n] There is no modifier to set the filename (existing syntax) but you gotta append the new modifier +n if you want effect.

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pwessel April 4, 2023, 5:13pm 10

I dont know what you mean here. obs is an array.

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