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Aug 19, 2013
08:20 PM

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Aug 19, 2013
08:20 PM

A question for the Mathcad historians

What Mathcad version and year did Odesolve first appear? This is not a test.

Solved! Go to Solution.

ACCEPTED SOLUTION

Accepted Solutions

Aug 20, 2013
01:27 AM

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Aug 20, 2013
01:27 AM

Harvey Hensley wrote:

What Mathcad version and year did Odesolve first appear?

Mathcad 2000.

See please http://twt.mpei.ac.ru/ochkov/Bridge/Bridge_eng.htm

16 REPLIES 16

Aug 19, 2013
09:34 PM

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Aug 19, 2013
09:34 PM

This is not a test.

That's a relief, because I would fail

Aug 20, 2013
01:27 AM

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Aug 20, 2013
01:27 AM

Harvey Hensley wrote:

What Mathcad version and year did Odesolve first appear?

Mathcad 2000.

See please http://twt.mpei.ac.ru/ochkov/Bridge/Bridge_eng.htm

Aug 20, 2013
10:23 AM

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Aug 20, 2013
10:23 AM

Thanks Valery. I saw a set of problems solved prio to that and I wondered why odesolve hadn't been used, then I suspected that it may not have been available.

Aug 21, 2013
05:10 AM

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Aug 21, 2013
05:10 AM

Harvey Hensley wrote:

You welcome!

Mathcad 2000 with odesolve can solve only one ODE- a Cauchy and boundary problems.

Mathcad 2001 can solve a system of ODEs too - but only a Cauchy problem.

But a boundary problem of ODEs with big error! Mathcad 15 and Mathcad Prime too

See please - t.end:=3

and t.end:=4

Aug 22, 2013
12:13 AM

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Aug 22, 2013
12:13 AM

Valery,

Unless you have some people dying, the sum of the sick and healthy should remain constant. Thus, their derivaties should be the same except for sign. I think if you get the rates corrected, odesolve will work fine.

Aug 22, 2013
01:15 AM

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Aug 22, 2013
01:15 AM

There are dead. This is one old model, which was solved back in the DOS versions of Mathcad on the difference scheme, and not through the solving ode.

Sorry Sick=x Healthe=y. A main is the wrong work of the odesolve by boundary problem solution.

Or I do someone wrong?

Aug 22, 2013
01:21 AM

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Aug 22, 2013
01:21 AM

There are dead. This is one old model, which was solved back in the DOS versions of Mathcad on the difference scheme, and not through the solving ode.

Sorry Sick (Больные) = x Healthe (Здоровые) = y. A main is the wrong work of the odesolve by boundary problem solution.

Or I do someone wrong?

Aug 22, 2013
07:50 AM

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Aug 22, 2013
07:50 AM

The problem appears to be that the system has more than one initial condition that can lead to the number of Sick at the end time. If instead you specify the initial Healthy and Sick and the final Dead, then the boundary solution is the same as the initial value solution. So I don't think it's really a problem with the solver, just a multiple answer system.

Aug 23, 2013
05:06 AM

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Aug 23, 2013
05:06 AM

Thanks!

But I think it is one YEMB!

The shooting method solves this problem.

Aug 23, 2013
06:35 AM

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Aug 23, 2013
06:35 AM

But I think it is one YEMB!

No! Here you see two different solutions to your problem. They both stick to the equations and adhere to your boundery condition. For the one is Sick(12)=209 in the upgoing branch before the maximum, for the other its after the max. But both are valid solutions to your problem. One method finds the one, another method finds the other. Harvey showed one way to force one particular solution by introducing a third function to the system.

Aug 23, 2013
07:31 AM

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Aug 23, 2013
07:31 AM

It wasn't the introduction of the Dead function alone. When I did that but still specified the Sick at tend, the result was still the solution to a different set of initial conditions. I checked those initial conditions by running as an initial value problem and they resulted in the right value for Sick(tend). Changing to specifying the Dead at tend produced the original solution to the initial value problem. Probably that specification has only one solution. The original specification definitely has more than one solution. I think it is just a fortunate coincidence that the shooting method gets the solution desired. Odesolve actually uses sbval (shooting method), but may have some different tolerance or initial step size?

Aug 23, 2013
07:55 AM

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Aug 23, 2013
07:55 AM

Harvey Hensley wrote:

It wasn't the introduction of the Dead function alone.

Yes, I was simplifying.

It looks to me that the original question has just a finite number of solutions, best guess: there are exactly two.

So it doesn't seem to be possible to add a constraint to the odesolve block to chose the desired one.

Things like Sick(0)>1 or Sick´(12)<0 obviously fail. So it looked to me that the skilled introduction of a third function would be the only way to do the job.

Aug 22, 2013
08:17 AM

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Aug 22, 2013
08:17 AM

The split happens when Sick is at its max.

Not sure if its really an error, as you wrote, or just another possible solution!?

EDIT: Let t.end-->infinity, so we get the conditions Healthy(0)=20000 and Sick(infinity)=0 and the constant solutions Sick(t)=0 and Healthy(t)=20000 will perfectly comply with your equations in a trivial way.

So, as Harvey has already pointed out, its just a multiple answer system, not YEMB (yet another mathcad bug).

Aug 27, 2013
10:35 AM

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Aug 27, 2013
10:35 AM

Werner Exinger wrote:

So, as Harvey has already pointed out, its just a multiple answer system, not YEMB (yet another mathcad bug).

By producing an analytical solution for Sick as a function of Health we can see more clearly the multiple solution aspect (see below, where I've used s for Sick and h for Health):

Actually, the situation is slightly more complicated than this - see attached file for more detail.

Alan

Edit: I posted this on 27 August. As of early 30 August it hasn't appeared.

Aug 31, 2013
05:07 PM

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Aug 31, 2013
05:07 PM

Edit: I posted this on 27 August. As of early 30 August it hasn't appeared.

Now I have no message from this forume...

Aug 31, 2013
08:55 PM

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Aug 31, 2013
08:55 PM

Valery Ochkov wrote:

Now I have no message from this forume...

Posting works now but will be delayed due to "moderation".

Go to this thread for more information http://communities.ptc.com/message/219570#219570