mehdi jafari

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7 years, 37 days

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These are replies submitted by mehdi jafari

@Mathematix u want the answer to the third question ?! but the problem are not the same.since u have written exp(-3) but it is exp(-3*x) . your answer seems to be somewhat simpler but for more skillful member i think.
but both are doing the same thing.

if you write it in this way,(exp(-3*x)) u can easily do this just like u said,without needing using subs command :

 

de := diff(y(x), `$`(x, 2))+4*y(x) = exp(-3*x);

 

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Download answer.mw

@Mathematix u want the answer to the third question ?! but the problem are not the same.since u have written exp(-3) but it is exp(-3*x) . your answer seems to be somewhat simpler but for more skillful member i think.
but both are doing the same thing.

if you write it in this way,(exp(-3*x)) u can easily do this just like u said,without needing using subs command :

de := diff(y(x), x$2)+4*y(x) = exp(-3*x);

Y := rhs(dsolve({de, y(0) = 2, (D(y))(0) = 0}, y(x)));

plot(Y, x = -1 .. 1);

de := diff(y(x), `$`(x, 2))+4*y(x) = exp(-3*x)

Y := (3/26)*sin(2*x)+(25/13)*cos(2*x)+(1/13)*exp(-3*x)

 

 

 

Download answer.mws

these variables are function of times , when i use a[1](0.0001) it means a[1] for the time t=0.0001:

i need to have them as a function of time , so i can not remove (i+h=0.0001).i even use subs to substitute a[i](t)=b[i] but it does not solve the problem, i really do not know what should i do ?!

and as far as i know, {seq(expr,k=1..18)} = {seq}(expr,k=1..18) . am i wrong?

these variables are function of times , when i use a[1](0.0001) it means a[1] for the time t=0.0001:

i need to have them as a function of time , so i can not remove (i+h=0.0001).i even use subs to substitute a[i](t)=b[i] but it does not solve the problem, i really do not know what should i do ?!

and as far as i know, {seq(expr,k=1..18)} = {seq}(expr,k=1..18) . am i wrong?

@Carl Love perfect,really nice.

can i have the answer of the desolve after the singular ponit ? so that i can find what happens in the singular point? and also can i know number of singular points ?

can i have the answer of the desolve after the singular ponit ? so that i can find what happens in the singular point? and also can i know number of singular points ?

what is the relation governing to P(i)s? if u say the relation,i think it is to easy to find the sum .

@rlopez thank u afterall, for your help and attention, as u said,Preben Alsholm always helps us with detailed answers and i am really thankful for his good help and good ideas,god bless u and him.thank u.

thank u for your discussion in here,and for your attention,
my problem is modeling a physical system and a real one,and if i change the initial conditions of the system,the parameters would change and maybe will be as u said,rescaled. but if i do that,my problem loses its physical face and changes to pure math which is not my aim to discuss.
setting some parameters to 0 is sth that can be invistageted, but i do not know what u mean by setting exponents to zero ? which exponents? 
but this kind of approach is perfect as for finding the problem with the equations,and thus i am really thankful for your idea for solving the problem.thank u.

thank u for your discussion in here,and for your attention,
my problem is modeling a physical system and a real one,and if i change the initial conditions of the system,the parameters would change and maybe will be as u said,rescaled. but if i do that,my problem loses its physical face and changes to pure math which is not my aim to discuss.
setting some parameters to 0 is sth that can be invistageted, but i do not know what u mean by setting exponents to zero ? which exponents? 
but this kind of approach is perfect as for finding the problem with the equations,and thus i am really thankful for your idea for solving the problem.thank u.

thanks for your detailed answer, i have another question ? why u said it is unwise to change the float point to 3 ? and what did u mean by keep theiir signs?
 i have another idea to say, maple solvers approximately awared me of the sort of the singular point since non of them does not solve the problem further, but i used step by step time integration method,and it does answered the problem, and my results  matched well with a CAE software. i actually do not know why this happens with maple solvers,and if it is a real singular one,why the other method solve it?

thanks for your detailed answer, i have another question ? why u said it is unwise to change the float point to 3 ? and what did u mean by keep theiir signs?
 i have another idea to say, maple solvers approximately awared me of the sort of the singular point since non of them does not solve the problem further, but i used step by step time integration method,and it does answered the problem, and my results  matched well with a CAE software. i actually do not know why this happens with maple solvers,and if it is a real singular one,why the other method solve it?

thanks for the answer,but my ode include the coefficients of one function, not the function itself,so i just need to use them and multiply them by x so that i can plot the function,and i could not do that with ode plot. thanks anyway.

thanks for the answer,but my ode include the coefficients of one function, not the function itself,so i just need to use them and multiply them by x so that i can plot the function,and i could not do that with ode plot. thanks anyway.

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