Drexel dragonThe Math ForumDonate to the Math Forum



Search All of the Math Forum:

Views expressed in these public forums are not endorsed by Drexel University or The Math Forum.


Math Forum » Discussions » Software » comp.soft-sys.matlab

Topic: populating a sparse matrix in mex
Replies: 1   Last Post: Nov 18, 2013 1:44 AM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]
Alexandre

Posts: 1
Registered: 11/16/13
populating a sparse matrix in mex
Posted: Nov 16, 2013 1:59 PM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

Hi everyone

I am having difficulties with populating sparse matrices. Here is my code:


//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

double *mxRES = NULL ; // output, i.e. first left hand side pointer
mwIndex *ir = NULL ;
mwIndex *jc = NULL ;
mwIndex entry_counter = 0 ;

[...]

// create lmax x kmax sparse matrix
plhs[0] = mxCreateSparse(lmax,kmax,Nelts, mxREAL) ;

mxRES = mxGetPr(plhs[0]) ;
ir = mxGetIr(plhs[0]) ;
jc = mxGetJc(plhs[0]) ;

for (k=0 ; k<kmax ; k++){

jc[(mwIndex)(k)] = entry_counter ;

for (l = 0 ; l<lmax; l++){


lll = some_function( l,k ) ;

// 'some_function' is a function with integer output between 0 and lmax-1

mxRES[entry_counter] = some_value ;
ir[entry_counter] = (mwIndex)(lll) ;
entry_counter++ ;
}
}

jc[ (mwIndex)(kmax) ] = entry_counter ;

////////////////////////////////////////////////////////////////////


my problem is that 'some_function( l )' is non-increasing with respect to l, i.e. some_function( l,k ) is not always greater than some_function( l' ,k) when l>l'. Therefore, for a given column k, when entry_counter is incremented, the row index is not always increasing. This results in some funny results, like if the output mxRES is a matrix X in matlab, then sometime we have [H']' =/= H.

I cannot change 'some_function( l,k )' to make it increasing w.r.t l. Is there any approach to tackle this problem? There must be one since the 'sparse' function in matlab does not require indices to be increasing

Thank you very much



Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© Drexel University 1994-2014. All Rights Reserved.
The Math Forum is a research and educational enterprise of the Drexel University School of Education.