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ptc-47354781-Visitor
1-Visitor
October 12, 2012
Solved

New mathcad prime 2.0 user need help on using the odesolve function

  • October 12, 2012
  • 2 replies
  • 6238 views

I am trying to solve a second order ODE in a solve block. I must have done something wrong with the syntax..

But I cannot figure out what is wrong, can anyone help?

It is just a simple calculation to find angular position as a function of time of a droping (rotating) plate which as one edge fixed to a rotation axis. And the force is gravity alone.

Thanks so much!

Best answer by ValeryOchkov

The corrected Mathcad Prime sheet in attach.

2 replies

V
ValeryOchkov24-Ruby IV
24-Ruby IV
October 12, 2012

All is OK in Mathcad 15:

ode-fi.png

Now I would like to find an error in Mathcad Prime - see about variables lables here http://communities.ptc.com/message/187832

V
ValeryOchkov24-Ruby IVAnswer
24-Ruby IV
October 12, 2012

The corrected Mathcad Prime sheet in attach.

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ptc-47354781-VisitorAuthor
1-Visitor
October 30, 2012

I am trying use root on the odesolve result. But I cannot , can someone let me know how to do it? It said it is out of the range.

Thanks

P
ptc-47354781-VisitorAuthor
1-Visitor
October 30, 2012

I can understand Valery's example, but I do not know what is wrong with mine. Can someone tell me? BTW, what is the difference between

1.jpg

and

2.jpg

When should I use a function(t) like Valery does in his example and when should I use the function at the end of my program?

Thanks

A
AlanStevens19-Tanzanite
19-Tanzanite
October 30, 2012

You can get it to work by replacing the dH(U,n,k,t)/dt term by the the gradient term as it appears in your ODE solve block (ie U.(1-k/H)^n or whatever it is). The results are values of time not values of the SOLVER function. However, what exactly are you trying to achieve here? The SOLVER function as it stands doesn't make much sense to me.

Alan

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ptc-47354781-VisitorAuthor
1-Visitor
October 30, 2012

Thanks, Now I get it.

Would you or anyone tell me the limitation of the derivative function? Like in this case, since I defined dH/dt = f(H(t)), I can replace it with f(H(t)) to do calculation. But in the case if I dont have f(H(t)) , I am forced to have mathcad calculate dH/dt, how can I avoid running into problem like what I had or how to spot a potential problem which would not allow me to use dH/dt directly?.

My function is to found a series of linear line that has a specified y-intercept and is tangent to the function of the curve fit, which is H(t). What I am really interested in is the slope of that line. So I first find where the linear line make tangent to H(t) and then find the value of that tangent slope. Can someone suggest a different way to do it? Or How should I write my program to skip finding "t" where the linear line is tangent to the curve and the solve for tangent slope? Is there a way to find the tangent slope I want directly?

What are other methods to acheive the same result? I want to learn more method

BTW, go back to my question about program.

When I define a function f(t) = some program,

what is the difference for using f(t) and f as the last line of entry in the program? Like in the two images I posted earlier, (the one with SOLVER(t) gives error, but the one with SOLVER work fine). But sometimes I see program ending in f(t), such as Valery's example

I am confused with their meaning.

Thanks

Henry

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