Re: [Help-glpk] FW: FW: Leap/OSeMOSYS

[Andrew Makhorin]

> Not sure if it is ok to address you with this issue, but I believe it
> does not really fit into the help distribution list. My question is
> just out of curiosity.

> We are currently working on an open source energy model
> www.OSeMOSYS.org, which is interlinked with an existing energy model
> called LEAP (www.energycommunity.org). LEAP in its new version can
> basically do optimization using OSeMOSYS and ultimately glpk. Some
> users set up an energy model with hourly time slices throughout the
> year, basically describing demand and generation for each and every
> hour of the year for a period of several years. This creates huge
> matices and glpk runs out of memory. Our colleagues tried then to use
> plexus, which was able to solve the problem in 30 seconds, which seems
> surprisingly short. 

> We were wondering what the main differences in the code are that
> explain this discrepancy.

The glp_prob problem object used on api level requires additional memory
to store various auxiliary information used by glpk routines. For
example, one element of the constraint matrix (of double type) being
stored in glp_prob requires 32 bytes (on a 32-bit platform) rather than
8 bytes. Thus, an lp instance being stored in glp_prob takes about four
times more memory than if it were represented as a set of plain arrays,
and about ten times more memory in case if the lp preprocessor is used.

To estimate the amount of memory required by glpk please see
http://lists.gnu.org/archive/html/help-glpk/2008-07/msg00044.html .

> Also, in case there is a generic option to make glpk solve this
> problem, apart from heavily adjusting the OSeMOSYS code, e.g., by
> splitting up the problem somehow, please do let us know.