RE: Mantain unevaluated

*To*: mathgroup at smc.vnet.net*Subject*: [mg14599] RE: [mg14551] Mantain unevaluated*From*: Daniel CLEMENT <dclement at mail.cpod.fr>*Date*: Mon, 2 Nov 1998 01:51:07 -0500*Sender*: owner-wri-mathgroup at wolfram.com

Guillermo, Have you tried to Hold[...] the calculation that you want to remain unevaluated? Daniel CLEMENT > ----- Original Message ----- > From: Guillermo de Paz [SMTP:guipaz at dali.eis.uva.es] > Sent: Friday, October 30, 1998, 9:07:25 > To: mathgroup at smc.vnet.net > Subject: [mg14551] Mantain unevaluated > > I'm using Mathematica to obtain the differential equations of some > mechanical systems and to integrate them numerically. When constructing > the equations I need to invert a matrix. This matrix is not very big > (lets say 8x8) but the elements al very long trigonometric expressions, > the inverse takes a long time. By the other side, it is possible that > for some values of the dependent variables the rank of the matrix is > not complete, and the size of the problem decreases. For these reasons > I would like to have unevaluated this inverse until the numerical > function NDSolve uses it (not to compute symbolically the matrix, but > compute it numerically inside NDSolve in each integration step). > I have done some attempts with := and with Compile, but I cant avoid the > symbolic computation of the inverse. Could somebody help me? > > Guillermo de Paz > Universidad de Valladolid. > e-mail: guipaz at dali.eis.uva.es > > > ----- End Of Original Message -----