[GiNaC-list] little optimization => lots of Memory usage

[James Jackson]

If I understand correctly, previously you were storing N strings, now you are storing N^2. This is 64M strings, as opposed to 8000. This might account for at least some of the memory!

Regards,
James

On 20 Oct 2010, at 16:45, Cristobal Navarro <axischire at gmail.com> wrote:

> Hello everybody,
> 
> i've been using ginac for some months and is very optimum, 
> but recently i've been facing a problem with the amount of memory used to store some expressions.
> i have a linear system of ecuations, with the size of around 8000 elements.
> 
> my first approach on building the matrix was use a map<string, ex*> where each element would correspond to a row element of the matrix.
> and all incognints of that row would be inside the expression ex. for a 4x4 system ecuaiton, the storage would be like this
> 
> <"certainKey1", ex1* > = B1*symbol2 + A1*symbol1 + D1*symbol4
> <"certainKey2", ex2*> = D2*symbol4 + B2*symbol2 + C2*symbol3
> <"certainKey3", ex3* > = B3*symbol2 + A3*symbol1 + D3*symbol4 + C3*symbol3
> <"certainKey4", ex4*> = A4*symbol1 + B4*symbol2 + C4*symbol3
> 
> this method was using an acceptable ammount of memory, around 15% of 32GB which was pretty good.
> the bad side of this approach was that when building the Ginac::matrix, i had to sort the elements and search each of them on their corresponding row, additionaly some where hidden because they had coefficient "0", so i had a list of symbols and on each row i searched for them, in a sorted way using the "coeff" method that Ginac provides.
> But i repeat, this was slow.
> 
> The point is that i decided to search for other solution, aiming on reducing the time needed to build the Ginac::Matrix.
> i came with the idea to use map< string, <string, ex> > mapMatrix, which is actually the matrix but sorted automatically because of the strings which are the incognits keyCode.
> now building the matrix is almost instant, no search needed, and all elements already sorted.
> 
> however, the program is using all the RAM = 32GB when doing the 8000x8000 problem.
> 
> i checked and rechecked for any memory leak, but havent found any so far, 
> 
> now the question = why did memory increase so much for just segmenting the expressions into separated smaller ones??
> is they same ammount of terms, just in separated sub-expressions., the ex object is too expensive??
> 
> 
> 
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