Incorrect definition for m.ln1p

[jthompson6]

The spec for the function
m.ln1p defines it as ln(1+ x^2). This is surprising because the normal definition, is ln(1+ x). This aligns with the classic Taylor series (the Mercator series) and java.lang.Math.log1p.

Looking at the code for hadrian, I see that the implementation is actually java.lang.Math.log1p.

I can verify this by running the PFA script

input: double
output: {type: array, items: double}
action:
  - new: [{m.ln1p: [input]}, {m.ln: [{+: [1, input]}]}, {m.ln: [{+: [1, {"**": [input, 2]}]}]}]
    type: {type: array, items: double}

and seeing the that the output for the first value matches the second, not the third.

So I think we should change the spec to say ln(1+ x).

[jthompson6]

Should I move this to https://github.com/datamininggroup/pfa?

[collinbennett]

Yes, please address any questions about the PFA specification to the DMG. You can use the github repo or the slack channel.

Thanks.

[jthompson6]

Okay, I've moved it, thanks.