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## Re: [Help-glpk] Basis matrix / sensitivity factors / sensitivity matrix

**From**: |
Andrew Makhorin |

**Subject**: |
Re: [Help-glpk] Basis matrix / sensitivity factors / sensitivity matrix |

**Date**: |
Mon, 5 Feb 2007 16:59:57 +0300 |

>* I am using GLPK to solve an LP model of an electricity network,*
>* and for one *
>* analysis we need to extract the sensitivity matrix. I don't know*
>* very much *
>* about linear programming, but I am told this is also known as the*
>* basis *
>* matrix.*
>
>* Is it possible to retrieve this information from GLPK, and if so*
>* what API *
>* routines do I need to use? It is not obvious to me from the API *
>* documentation, but that may just be because I am not very*
>* familiar with the *
>* terminology of linear programming.*
Probably you mean not the basis matrix, but the simplex tableau,
i.e. the matrix which shows how basic variables depend on non-basic
ones: xB = (alfa[i,j]) * xN. If so, you can compute it by rows or
by columns using api routines lpx_eval_tab_row and lpx_eval_tab_col.
For more details see the glpk user's manual.
If you intend using that matrix to perform post-optimal sensitivity
analysis, look at the routines in file src/glplpx8b.c.