Tips

Some suggestions from the HANDE developers for using HANDE…heed our words!

Compilation

For optimised versions of HANDE, explore using:

• compiler-specific optimisation flags

  In general adding ‘high-level’ optimisation flags (-O3, -Ofast, etc.) makes a substantial impact on the calculation speed.

• interprocedural optimisation

  Many compilers can perform interprocedural optimisation, whereby optimisations are performed at link-time instead of compile-time. This allows optimisations to be performed (including inlining) on procedures specified in different source files. On some compilers (e.g. GCC, Intel) this can have a substantial benefit; on other compilers the difference is less marked.

• popcnt instruction

  If the processor being used includes it, uses the popcnt instruction rather than a software implementation to count bits set in an integer. This can have a impact of the order of a few percent for the entire calculation.

• DET_SIZE=64

  Use 64-bit integers rather than 32-bit integers to store the representation of the determinant/excitor/tensor labels. This can make certain calculations quicker (i.e. those involving more than 32 single-particle basis functions) by reducing the amount of bit operations that need to be performed.

Plotting calculation output using gnuplot

The first section of the output file contains information about the basis functions used in the calculations. This gives spurious data points when the contents of the file is plotted using gnuplot. They can be removed by creating an executable file called gphande in the user’s $PATH, containing:

#!/bin/sed -nf
1,/iterations/d
/^ *[0-9]/p

When plotting in gnuplot, using the command

plot '<gphande file'

instead of

plot 'file'

will then remove the extra points.