[Os-project-managers] Question about OSxLParserdata, OSInstance, OSOption

[Kipp Martin]

Hi Gus:
> 
> I probably should have asked this long ago, but I never really took  
> everything on board and then I forgot.

First, a generic comment. One I have made before. OS is a project 
evolving over time. Much of what you see in OSInstance was written four 
years ago. My guess is that if you were to work on the OSoL parser four 
year from now you might do things differently. The OS constitution was 
not written on day 1 and then adhered to from day 1 over time. It 
evolved and is evolving. We are constantly learning new and better ways 
to do things. I knew almost no C++ when I first started OS.

Now, with regard to the m_mxxx. Let's take as an illustration, 
m_mdVariableLowerBounds.  Remember, Object Orient Programming makes 
things SLOW. There is definitely a performance hit. Indeed we are really 
getting clobbered with this in the nonlinear part of our code. So let's 
look at for example, the method to get the variable lower bounds. Here 
it is:


double* OSInstance::getVariableLowerBounds() {
	processVariables();
	return m_mdVariableLowerBounds;
}//getVariableLowerBounds

Look how efficient and fast it is. You are just returning a C-pointer to 
a chunk of memory. You don't have to go through the nonsense of looping 
over multiple objects like this:

instanceData->variables->var[i]->lb;

for each i. Ouch, the above is going to be comparatively slow. Memory is 
cheap. Why not duplicate in-memory the variable lower bounds so they can 
accessed more efficiently?  Now let's say you want to get this 
information over and over again many times. Using the 
m_mdVariableLowerBounds is going to the be the most efficient way to do 
this. Right now I am trying to finish up a project for the Cincinnati 
folks that involves decomposition and branch and price. I am constantly 
accessing row and variable upper bounds and resetting them. Working 
directly with pointers that have the information in memory is the most 
efficient way to do this.

Jun -- anything to add?

Cheers


> 
> Only today do I realize (again) that there is quite a difference in  
> the things that are being stored in OSInstance and OSOption.  
> OSInstance stores the entire instance into arrays and things and then  
> duplicates everything into the OSInstance object. This seems wasteful  
> to me, so I have in the OSoL parser been far more conservative and  
> stored _nothing_ into m_mi... things. I store stuff into  
> OSoLParserdata temporarily, and then copy them into the OSOption  
> instance, upon which I will free the temporary storage in  
> OSoLParserdata. OSResult and OSrLParserdata do things that way, too,  
> and maybe that is where I picked up my habits.
> 
> I hope I am respecting the constitution. (I have not found anything  
> about it in the statutes, so I am not sure.)
> 
> Cheers
> 
> gus
> 
> 
> 
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-- 
Kipp Martin
Professor of Operations Research
and Computing Technology
Booth School of Business
University of Chicago
5807 South Woodlawn Avenue
Chicago, IL 60637
773-702-7456
kmartin at chicagobooth.edu
http://www.chicagobooth.edu/faculty/bio.aspx?person_id=12825325568
http://projects.coin-or.org/OS