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Ruby I

## IF in Given-Odesolve

Can we use IF in the Given-Odesolve Block?

See please the red operator in attach!

21 REPLIES 21

## Re: IF in Given-Odesolve

Try the step function (PHI)...

Success!
Luc

## Re: IF in Given-Odesolve

Can't see your sheet, but here:

## Re: IF in Given-Odesolve

@ValeryOchkov wrote:

Can we use IF in the Given-Odesolve Block?

Yes, we can! 🙂

The problem is not the if-function you used.

The error message says something about an unstable problem resulting in a step size too small and suggests that you reduce the integration interval.

If you follow this suggestion and set t.end to 0.5 the solve block perfectly works.

Looks like the solution curve has a tendency you shoot up vertically at the new end value which makes the solve block fail if t.end is larger:

## Re: IF in Given-Odesolve

Thanks, I see

I use not if in attach.

## Re: IF in Given-Odesolve

@ValeryOchkov wrote:

Thanks, I see

I use not if in attach.

Yes, but thats not equivalent, thats a completely different function .

As already written above, the if function is NOT the problem.

E.g. you may use

with success, but if you use lower values than 66.323N for "limit", the block gets too unstable and fails.

## Re: IF in Given-Odesolve

Thanks, Werner!

But what about the logistic function in attach (Prime)

## Re: IF in Given-Odesolve

@ValeryOchkov wrote:

Tanks, Werner!

But what about the logistic function in attach (Prime)

It seems to have the same problem (the error message in Prime is less specific).

Your question was, if the "if" function can be used in the odesolve-block and the answer clearly is a "Yes".

The error was not because of the if function but is due the setup and modelling of your problem in general as your new example with the logistic function shows.

## Re: IF in Given-Odesolve

One solution in attach (Prime).

Questions:

• How calculate the potential energy of the link?
• Why we have an error on the board from the elastic to hard link?
• Can we use the logistic function?

## Re: IF in Given-Odesolve

There is a unit mismatch when you add the signals:

## Re: IF in Given-Odesolve

Yes! The formula is wrong! I need a correct one!

The sum of three kind of energy must be constant!

## Re: IF in Given-Odesolve

Hi,

In my opinion the mistake is in the definition of the elastic constant: the units are N/m=kg/s^2.

Bye bye

## Re: IF in Given-Odesolve

I agree that the additional factor x in the integral (pe2) was wrong and caused the unit mismatch.

## Re: IF in Given-Odesolve

Hi,

In my opinion the mistake is in the definition of the elastic constant: the units are N/m=kg/s^2.

Bye bye

## Re: IF in Given-Odesolve

Thanks!

But the sum of 3 types of energy must be constant!

See please the case with the linear Hook law

## Re: IF in Given-Odesolve

Утро вечера мудренее! I go to bet!

## Re: IF in Given-Odesolve

You have to redo everything

Спокойной ночи

## Re: IF in Given-Odesolve

я надеюсь, что мне ночью приснится решение этой красивой задачи, как Менделееву приснилась таблица химических элементов

## Re: IF in Given-Odesolve

They say that the periodic table was first dreamed of by Pushkin,  but he did not understand anything in it!

## Re: IF in Given-Odesolve

I saw at night in a dream that there we can have in the solve block not four, but three functions!

But I did not see the correct formula for calculating the potential energy of an elastic link with the non-linear Hooke law 😞

And still no one told me in a dream why we cannot work in the not elastic region of Hooke's nonlinear law.

😞

😞

😞

## Re: IF in Given-Odesolve

This apple needs to fall on one of us on the head!

## Re: IF in Given-Odesolve

Доброе утро!

In general, we try to understand something when something is wrong. You could "waste" a few words, to say that in the worksheet you use "spring compliance" and not "spring stiffness".

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