System of differential equations

*To*: mathgroup at smc.vnet.net*Subject*: [mg13511] System of differential equations*From*: Jaume Terradas <jaume at hubble.uib.es>*Date*: Fri, 31 Jul 1998 04:33:26 -0400*Organization*: Universitat de les Illes Balears*Sender*: owner-wri-mathgroup at wolfram.com

Dear Sirs, When I want to eliminate a variable of a system of DEQ, I can't eliminate its derivatives: In[1]:= Eliminate[{a y[z]-b s'[z]==0,d s[z]+f y'[z]+g s'[z]+h s''[z]==0},{y[z]}] Out[1]:= d s[z]== -g s'[z]-f y'[z]-h s''[z] depends on y'[z] when in fact it is possible to eliminate it deriving the first equation and putting them in the second one. I will agree any help. Jaume