On 10-07-2013, at 20:42, Berend Hasselman <b...@xs4all.nl> wrote: > > On 10-07-2013, at 16:21, Raphaëlle Carraud > <raphaelle.carr...@oc-metalchem.com> wrote: > >> Bonjour, >> >> Je souhaite résoudre le couple d'équation différentielles suivant : >> >> 0 = -dA + dB + 2*dC - 2*r1 - 2*r5 >> 0 = dA + dD + r1 + r4 >> 0 = K2 - C/B^2 >> 0 = K3 - D/(A*B) >> >> 0 = r5 + 2*r4 - dE >> 0 = r5 -dI >> 0 = -r5 - r4 - dG >> 0 = -r1/2 - dH >> >> en ayant connaissance des valeurs initiales de dA, dB, dC, dE, dI, dG, dH, >> r1, r2, r4, r5, K2, K3, A, B, C et D. >> > > If all initial values are known then plugging the values in the system will > give 0 or not 0. There is nothing to "solve". > >> J'ai essayé plusieurs fonctions mais comme je ne peux pas lui faire calculer >> une des dérivée de laquelle découlerait les autre, il n'arrive pas à me >> fournir la solution. >> Je n'ai pas vu d'exemple qui pourrai s'assimiler à celui-ci dans la >> documentation. >> > > You will have to redo your query in English. Questions in French won't > receive many replies. > My French is rudimentary but I'll try. > > You have 8 equations and 17 variables. > So how do you propose to "solve" the system? > > Assuming that the d? variables are differentials and that you want to solve > for those: > you have 7 of these and 8 equations. So how to solve? > > But the third and fourth equations have no d? variables, so the may even be > inconsistent given the values of K2, K3, C, B, A, D. > So you have 6 equations for 7 d? variables. So how do you propose to solve > for the d? variables? > > Finally your system seems to be linear in the d? variables. You would be able > to use R's solve() if you can get your system to be a square system. > > If your system is not square and underdetermined then you can use a Moore > Penrose inverse to get a minimum norm solution > (http://en.wikipedia.org/wiki/Moore–Penrose_pseudoinverse#Minimum-norm_solution_to_a_linear_system). > package MASS provides a function ginv().
And to make matters simple: since your lefthand sides are 0 the minimum norm solution of your system is 0. Berend ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
