Parameters defined by (static) equations

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HUisman
Posts: 31
Joined: Wed Sep 21, 2005 8:48 am

Parameters defined by (static) equations

Postby HUisman » Fri Mar 03, 2006 12:41 pm

Is it possible to implement the possibility to assign a static equation (even with predifined constants like pi ) when defining a parameter?

So

parameters

real force = 10 {N};
real ratio = 10/37;
real diameter = 2*pi*10 {m};

paul
Posts: 152
Joined: Mon Sep 19, 2005 2:00 pm
Location: Controllab Products B.V.

Re: Parameters defined by (static) equations

Postby paul » Tue Apr 25, 2006 9:10 am

HUisman wrote:Is it possible to implement the possibility to assign a static equation (even with predifined constants like pi ) when defining a parameter?

So

parameters

real force = 10 {N};
real ratio = 10/37;
real diameter = 2*pi*10 {m};


We're are testing this at the moment.
member 20-sim development team

Ludo Visser
Posts: 51
Joined: Wed Sep 28, 2005 10:13 pm

Re: Parameters defined by (static) equations

Postby Ludo Visser » Wed Feb 08, 2012 5:39 pm

This is still not working (nearly 6 years later). Are there any plans to include this in near-future versions? Would be very nice.

paul
Posts: 152
Joined: Mon Sep 19, 2005 2:00 pm
Location: Controllab Products B.V.

Re: Parameters defined by (static) equations

Postby paul » Thu Feb 09, 2012 12:09 pm

Ludo Visser wrote:This is still not working (nearly 6 years later). Are there any plans to include this in near-future versions? Would be very nice.


Perhaps there is a nice work-around (that is present since 20-sim 4.0) that was written for parameter relations:
You can assign parameters in the initialequations and finalequations as well, so

Code: Select all

mass = volume * density;

is a valid assignment in these sections when all three are parameters.
member 20-sim development team

Ludo Visser
Posts: 51
Joined: Wed Sep 28, 2005 10:13 pm

Re: Parameters defined by (static) equations

Postby Ludo Visser » Thu Feb 09, 2012 1:36 pm

Does this imply that the value for "mass" is overwritten, regardless of what value you give it? Doesn't this imply that "mass" is a variable rather than a parameter?
Maybe I'm missing something, but I cannot see why this is a workaround.

Ludo Visser
Posts: 51
Joined: Wed Sep 28, 2005 10:13 pm

Re: Parameters defined by (static) equations

Postby Ludo Visser » Thu Feb 09, 2012 1:53 pm

Ludo Visser wrote:I cannot see why this is a workaround.


Maybe I can clarify this with an example. Let's assume that I need the area of a circle with known radius as a parameter to my model. The "workaround" requires that I make two parameters: one for the radius, say R, and one for the area, say A:

Code: Select all

parameters
    real R = 2.0 {m};
    real A = 0.0 {m^2};    // According to Paul, it does not matter what value I put here
initialequations
    A = pi*R^2;


How I do it now (which I believe is the correct way, since A is not really a parameter):

Code: Select all

parameters
    real R = 2.0 {m};
variables
    real A;
initialequations
    A = pi*R^2;


The "workaround" doesn't really help anything, but only adds confusion because the assigned value for A is overwritten.

What Huisman and I would like to do is:

Code: Select all

parameters
    real A = pi*2.0^2 {m^2};

Instead of having to pre-calculate A:

Code: Select all

parameters
    real A = 12.566370614 {m^2}

paul
Posts: 152
Joined: Mon Sep 19, 2005 2:00 pm
Location: Controllab Products B.V.

Re: Parameters defined by (static) equations

Postby paul » Fri Feb 17, 2012 1:04 pm

Maybe I can clarify this with an example. Let's assume that I need the area of a circle with known radius as a parameter to my model. The "workaround" requires that I make two parameters: one for the radius, say R, and one for the area, say A:

Code: Select all

parameters
    real R = 2.0 {m};
    real A = 0.0 {m^2};    // According to Paul, it does not matter what value I put here
initialequations
    A = pi*R^2;



The parameter A does not need to have a value in this case, since there is a parameter relation that assigns it.
It still is a parameter, since it does not change over time during the simulation. This is the work around:

Code: Select all

parameters
    real R = 2.0 {m};
    real A {m^2};
initialequations
    A = pi*R^2;
member 20-sim development team

sabahat
Posts: 1
Joined: Thu Nov 06, 2014 10:24 am

Re: Parameters defined by (static) equations

Postby sabahat » Thu Nov 06, 2014 1:50 pm

I found them, thanks! This is great work, and will save me a lot of effort. :)
Are you worried about LX0-102 questions exam prep and IFPUG


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