ODE solve help : predefine a function

[math]

Hi,

It would be super great to have any suggestions for the mathcad file I have attached.. Please check the file, I have described it there..

Thanks!

[Werner_E]

Not sure if I understand correctly what you want to achieve,

I wonder why you would want to introduce a third unknown function in the solve block which is dependent in a simple way on the function N.p which you are solving for.

Are you looking for something like this:

[Fred_Kohlhepp]

How about this??

[Werner_E]

I guess the initial value of M.p should not be 1 but 30 ((1-delta2)*P.N.)

But I wonder why the result is so much different!?

EDIT: I felt into the same trapdoor. It should rather be like this:

[math]

i think the picture is not attached well.. I cannot see it..

[Werner_E]

preeti baskaran wrote:

i think the picture is not attached well.. I cannot see it..

This unfortunately happens ever so often.

Hope it works this time:

[math]

Hi,

I think it is getting a bit deviated from i want to achieve.. I don't want to add an extra M.p on the ODE block, I am only trying to simplify my equations.

What i trying to achieve is to make the C.p(t) equation look a bit simple by shrinking ((1-delta2)*P.N' N.p(t)) into one variable such as M.p(t).

such as to predefine a variable,

M.p(t) = (1-delta).P.N*N.p(t)

So that,

C.p(t) = M.p(t) - µ.pCp(t)

or if this is possible?

[Werner_E]

Look at Fred's post and the picture I just posted a second time.

Or maybe the second pic in my first replay, if you still want to solve for N.p and not M.p.

[math]

But.. did u read the post that i replied recently?

I wonder why you would want to introduce a third unknown function in the solve block which is dependent in a simple way on the function N.p which you are solving for.

Are you looking for something like this:

I dont want to introduce a third unknown function, I would just like to simplify my equations by predefining them

[Fred_Kohlhepp]

Go read the sheet I posted.

You can do a simple modification of your solve block allows M (t) instead of N (t). There is some question about boundary conditions.

[Werner_E]

Fred Kohlhepp wrote:

Go read the sheet I posted.

You can do a simple modification of your solve block allows M (t) instead of N (t). There is some question about boundary conditions.

I still think that your equation is wrong. You should not divide by (a-delta2)*P.N but multiply - see here: http://communities.ptc.com/message/261074#261074

[Fred_Kohlhepp]

Werner Exinger wrote:

I still think that your equation is wrong. You should not divide by (a-delta2)*P.N but multiply - see here: http://communities.ptc.com/message/261074#261074

Werner;

Attached is my logic. Show me!

[Werner_E]

Fred Kohlhepp wrote:

Werner Exinger wrote:

I still think that your equation is wrong. You should not divide by (a-delta2)*P.N but multiply - see here: http://communities.ptc.com/message/261074#261074

Werner;

Attached is my logic. Show me!

Her is mine

[Fred_Kohlhepp]

You're right!!

Don't know where my head was at.

[math]

Thanks and I appreciate your valuable solutions.. but I feel its is only making the equations complicated...

[Fred_Kohlhepp]

preeti baskaran wrote:

Thanks and I appreciate your valuable solutions.. but I feel its is only making the equations complicated...

It's not making it complicated; it's doing what you asked--replacing Np(t) with Mp(t)

You can combine these two equations into a single second order ODE in Cp, and solve it via Laplace transfer. For the parameters values you gave, you get the same solution.

I'm done.

[AlanStevens]

Attached is another analytical solution, together with the resulting numerical values using your input data (some of the numerical constants are slightly different from Fred's).

Alan

PS Are you sure you've got the all the signs right?

[Werner_E]

preeti baskaran wrote:

But.. did u read the post that i replied recently?

I wonder why you would want to introduce a third unknown function in the solve block which is dependent in a simple way on the function N.p which you are solving for.

Are you looking for something like this:

I dont want to introduce a third unknown function, I would just like to simplify my equations by predefining them

Yes, I read your reply - did you read ours? Neither my second approach in my first reply nor Fred's approach uses a third unknown function. The choice is if you will use your M.p instead of N.p (and so also solve vor M.p) and use Freds approach or if you like to use M.p as an abbrevation but still want to solve for N.p - then my second approach (where M.p is dependent on t AND N.p(t)) may help.