## 584 Reputation

7 years, 218 days

## define a function for the derivative var...

i have an ode,which its derivatives are with respect to time,i want to use the output as a function of time to use it in a loop ,what should i do ?!

A:=a*diff(x(t),t,t)+b*diff(x(t),t)+c*x(t);

B:=solve(A,diff(x(t),t,t));

at first how can i define B as a function of t here?
how can i define initial conditons for this ?
for example :
a0:=diff(x(t),t,t) at time 0 (x(0)), but i do not know how to define this?

i also can not use B in a loop of time,t

## output=listprocedure...

when solving using output=listprocedure i face this message :

Sys:= {seq}(eq[k], k= 1..18):

fsolve(Sys, {seq}(a[k], k= 1..18),output=listprocedure):

Error, (in fsolve) output = listprocedure is an invalid option

what should i do? how can i list my output to use in latter commands? for example i want to use the output of the problem to plot an expression that the outputs are the coefficients of that expression?

## solve nonlinear system,...

i want to solve these equations to find the 18 coefficents,how should i solve them to solve it in minimum time possible?

eq(1):= -2144447222.22*a(7)-1531751031.75*a(8)-1148816190.48*a(9)-584858207.070*a(12)-5003703703.71*a(18)-714823743.386*a(11)-893526455.026*a(10)-5361111111.11*a(17)-5744047619.05*a(16)-6433333333.35*a(13)-6433333333.34*a(14)-6126984126.99*a(15);

eq(2):=-1531747698.41*a(7)-1148812857.14*a(8)-4288888888.90*a(13)-4595238095.25*a(14)-4595238095.24*a(15...

## dsolve,numeric takes more than 12 hours...

hi, i have solved my equations with dslove numeric,with 3 terms approximations,it takes maybe 5 minutes to solve it,when i increase 3 terms to 4,it takes more than a day to solve,however my queation is about another problem,
i solved my equations with 3 terms approximation (in 5 minutes),when i want to get answers , for the very little times (i,g=0.00001) it answer quickly,but now i am calculating it for  t=1 seconds and it takes more than 12 hours to answer and it...

## taking variation of equations...

i have some equations,and i want use them in the Hamilton's principle to drive my my equations,can i use maple to take variations?thanks for your help and attentions,

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