The recursion of Legendre polynomials and tensor harmonics during the analysis and synthesis of HEALPix maps can be time consuming. Especially when repetitive applications are desired there is no need to compute the recursions every time. For such applications the values of can be precomputed with plmgen and stored in a file. When using synfast or anafast this file can be read in to shorten the analysis/synthesis execution time.
The memory (and disc) consumption of plmgen is bytes, with and Np is either 1 or 3, depending whether tensor harmonics are computed.
Currently an extra limitation also applies, corresponding to, eg, lmax for nsmax =1024.
plmgen runs in interactive mode, self-explanatory.
When `filename' is present, plmgen enters the non-interactive mode and parses its inputs from the file `filename'. This has the following structure: the first entry is a qualifier which announces to the parser which input immediately follows. If this input is omitted in the input file, the parser assumes the default value. If the equality sign is omitted, then the parser ignores the entry. In this way comments may also be included in the file. In this example, the file contains the following qualifiers:
- Initial release HEALPix 1.00
|can not allocate memory for array xxx||Fatal||You do not have sufficient system resources to run this facility at the map resolution you required. Try a lower map resolution.|
|Error: these values of Nside and l_max are too large||Fatal||You are exceeding the limitation on Nside and l_max. Try a lower l_max.|
Version 3.31, 2017-01-06