The behavior you see for MinimalExample.example and MinimalLibrary.Example are bugs, and from what I can see they should work, I have forwarded them to a developer working on these things.

As for the validation of MinimalLibrary.Components.SimpleClock, what happens is that you have an outer component (outer constant String unitOfTime). The rules for inner/outer in Modelica (this was updated recently) is that an outer element requires that an inner element exists or can be created in a unique way. In this case, there exists no inner element, but a unique inner element can be created, by simply taking the outer declaration as it is (this is basically what the first warning says). The second warning appears because the constant has no binding (although I am not sure why it is referred to as a parameter).

We have recently implemented some support for setting the displayUnit for the x-axis in SimulationCenter, currently it only goes up to days, maybe we should see if we could add years as well. I guess you would like a way to specify this in the model so you don't have to change the plots all the time.

As for the parameters in the diagram view, I assume you are referring to things like this:

which seems to always use the unit. So, it would be better for you if it was displayed in the displayUnit, maybe with the displayUnit as well? So, in the picture above, it would read "J = 1.7 kgm^2", or if the displayUnit was changed to lb ft^2, it would say "J = 40.34 lb ft^2".

It might be that I don't know enough about what you are modeling, but it seems to me that an output of a specific block would be either dimensionless, a rate or time, and for a specific block you don't really want to change it?

In the package below I have demonstrated some ways to set units in the GUI, and the model Test shows all four of them.

The block Item has an output that is something, e.g. "orange". What this is is set by the constant itemUnit, which shows up in the GUI in the "General" tab in the group "Units" (this is set by the annotation following the declaration of itemUnit).

The block Rate has an output that is a rate of something, e.g. "apple/s". You can set what "X" in "X/s" through the"rateUnit constant, which also shows up in the GUI. Here I have also set a displayUnit to be "X/h", but since we don't have the feature described in my last post, SimulationCenter won't be able to display in "X/h" unless X is 1.

In the block Generic I have done something like what you described. The block output has a unit that is either "1", "s" or "1/s", and this can be chosen with a drop-down list. The drop-down list is created from the choices part of the annotation after the declaration of the output, each which has a part that is the modification to be applied (e.g. "= 1/s") and a description of what it is (e.g. "rate"). The description is what is shown in the drop-down menu.

Finally, in the block GenericWithX you can specify both a base unit (e.g. "banana" or "second") and specify it is a rate or not.

Concerning your PS, yes, that would in principle be what it would do; read "X/s", then use for example,the rule for "1/s" -> "1/year" to convert to "X/year".

package UnitsAndRates
  model Test
    Item item1(itemUnit = "apple") annotation(Placement(visible = true, transformation(origin = {-30, 57.954}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
    Rate rate1(rateUnit = "orange") annotation(Placement(visible = true, transformation(origin = {-10, 10}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
    Generic generic1(genericUnit = "1/s") annotation(Placement(visible = true, transformation(origin = {-65, -40}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
    GenericWithX genericWithX1(base = "banana") annotation(Placement(visible = true, transformation(origin = {50, -2.046}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
    GenericWithX genericWithX2(base = "kiwi", rate = "/s") annotation(Placement(visible = true, transformation(origin = {30, -62.465}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
    annotation(Diagram(coordinateSystem(extent = {{-150, -90}, {150, 90}}, preserveAspectRatio = true, initialScale = 0.1, grid = {5, 5})), Icon(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {10, 10}), graphics = {Rectangle(visible = true, lineColor = {0, 114, 195}, fillColor = {255, 255, 255}, extent = {{-100, -100}, {100, 100}}, radius = 25), Text(visible = true, textColor = {64, 64, 64}, extent = {{-150, 110}, {150, 150}}, textString = "%name")}));
  end Test;

  block Rate
    constant String rateUnit = "1" annotation(Dialog(group = "Units"));
    Modelica.Blocks.Interfaces.RealOutput y(unit = rateUnit + "/s", displayUnit = rateUnit + "/h") annotation(Placement(visible = true, transformation(origin = {155, 0}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {101.511, 0}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  equation
    y = 1 + cos(sin(time));
    annotation(Diagram(coordinateSystem(extent = {{-150, -90}, {150, 90}}, preserveAspectRatio = true, initialScale = 0.1, grid = {5, 5})), Icon(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {10, 10}), graphics = {Rectangle(visible = true, lineColor = {0, 114, 195}, fillColor = {255, 255, 255}, fillPattern = FillPattern.Solid, extent = {{-100, -100}, {100, 100}}), Text(visible = true, textColor = {64, 64, 64}, extent = {{-150, 110}, {150, 150}}, textString = "%name"), Text(visible = true, origin = {-0, 3.332}, extent = {{-100, -46.668}, {100, 46.668}}, textString = "Rate")}));
  end Rate;

  block Item
    constant String itemUnit = "1" annotation(Dialog(group = "Units"));
    Modelica.Blocks.Interfaces.RealOutput y(unit = itemUnit, displayUnit = itemUnit) annotation(Placement(visible = true, transformation(origin = {153.595, 0}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {102.397, 0}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  equation
    y = 1 + cos(sin(time));
    annotation(Diagram(coordinateSystem(extent = {{-150, -90}, {150, 90}}, preserveAspectRatio = true, initialScale = 0.1, grid = {5, 5})), Icon(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {10, 10}), graphics = {Rectangle(visible = true, lineColor = {0, 114, 195}, fillColor = {255, 255, 255}, extent = {{-100, -100}, {100, 100}}, radius = 25), Text(visible = true, textColor = {64, 64, 64}, extent = {{-150, 110}, {150, 150}}, textString = "%name"), Text(visible = true, extent = {{-100, -40}, {100, 40}}, textString = "Item")}));
  end Item;

  block Generic
    constant String genericUnit = "1" annotation(Dialog(group = "units"), choices(choice = "1" "dimensionless", choice = "s" "time", choice = "1/s" "rate"));
    Modelica.Blocks.Interfaces.RealOutput y(unit = genericUnit) annotation(Placement(visible = true, transformation(origin = {155, 0}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {103.333, 0}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  equation
    y = 1 + sin(cos(sin(time)));
    annotation(Diagram(coordinateSystem(extent = {{-150, -90}, {150, 90}}, preserveAspectRatio = true, initialScale = 0.1, grid = {5, 5})), Icon(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {10, 10}), graphics = {Rectangle(visible = true, lineColor = {0, 114, 195}, fillColor = {255, 255, 255}, fillPattern = FillPattern.Solid, extent = {{-100, -100}, {100, 100}}), Text(visible = true, textColor = {64, 64, 64}, extent = {{-150, 110}, {150, 150}}, textString = "%name")}));
  end Generic;

  block GenericWithX
    constant String base = "1" annotation(Dialog(group = units));
    constant String rate = "" annotation(Dialog(group = units), choices(choice = "" "not rate", choice = "/s" "rate"));
    Modelica.Blocks.Interfaces.RealOutput y(unit = base + rate) annotation(Placement(visible = true, transformation(origin = {156.679, 0}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {101.922, -2.301}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  equation
    y = 1 + sin(sin(time));
    annotation(Diagram(coordinateSystem(extent = {{-150, -90}, {150, 90}}, preserveAspectRatio = true, initialScale = 0.1, grid = {5, 5})), Icon(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {10, 10}), graphics = {Rectangle(visible = true, lineColor = {0, 114, 195}, fillColor = {255, 255, 255}, fillPattern = FillPattern.Solid, extent = {{-100, -100}, {100, 100}}), Text(visible = true, textColor = {64, 64, 64}, extent = {{-150, 110}, {150, 150}}, textString = "%name"), Text(visible = true, origin = {1.009, 0.32}, extent = {{-101.009, -99.68}, {101.009, 99.68}}, textString = "X")}));
  end GenericWithX;
  annotation(Diagram(coordinateSystem(extent = {{-150, -90}, {150, 90}}, preserveAspectRatio = true, initialScale = 0.1, grid = {5, 5})), Icon(coordinateSystem(extent = {{-100, -100}, {100, 100}}, preserveAspectRatio = true, initialScale = 0.1, grid = {10, 10}), graphics = {Polygon(visible = true, origin = {0.248, 0.044}, lineColor = {56, 56, 56}, fillColor = {128, 202, 255}, fillPattern = FillPattern.Solid, points = {{99.752, 100}, {99.752, 59.956}, {99.752, -50}, {100, -100}, {49.752, -100}, {-19.752, -100.044}, {-100.248, -100}, {-100.248, -50}, {-90.248, 29.956}, {-90.248, 79.956}, {-40.248, 79.956}, {-20.138, 79.813}, {-0.248, 79.956}, {19.752, 99.956}, {39.752, 99.956}, {59.752, 99.956}}, smooth = Smooth.Bezier), Polygon(visible = true, origin = {0, -13.079}, lineColor = {192, 192, 192}, fillColor = {255, 255, 255}, pattern = LinePattern.None, fillPattern = FillPattern.HorizontalCylinder, points = {{100, -86.921}, {50, -86.921}, {-50, -86.921}, {-100, -86.921}, {-100, -36.921}, {-100, 53.079}, {-100, 103.079}, {-50, 103.079}, {0, 103.079}, {20, 83.079}, {50, 83.079}, {100, 83.079}, {100, 33.079}, {100, -36.921}}, smooth = Smooth.Bezier), Rectangle(visible = true, origin = {0, -5}, lineColor = {198, 198, 198}, fillColor = {238, 238, 238}, pattern = LinePattern.None, fillPattern = FillPattern.Solid, extent = {{-100, -25}, {100, 25}}), Polygon(visible = true, origin = {-0, -10.704}, lineColor = {113, 113, 113}, fillColor = {255, 255, 255}, points = {{100, -89.296}, {50, -89.296}, {-50, -89.296}, {-100, -89.296}, {-100, -39.296}, {-100, 50.704}, {-100, 100.704}, {-50, 100.704}, {0, 100.704}, {20, 80.704}, {50, 80.704}, {100, 80.704}, {100, 30.704}, {100, -39.296}}, smooth = Smooth.Bezier)}));
end UnitsAndRates;

Carl,

Thank you for confirming the impression I had about the examples given. Making these things work out in WSM would be very helpful. The warning (besides falsly referring to a parameter) given for the outer declarationg does make sense as we talk about it. It may be better to work with inner outer instead if one cannot be sure about when and where eventually an inner construct is placed?

With regard to displayUnit it would be nice, if this could be influenced globally (maybe then to be overriden by user choice?) in a model for:

• display of time in plots
• display of parameters in icon- and diagram-view
• actually, any output of model entities and possibly also for inputs (cf. Time Scale parameter for MCTT)...

Regarding the conversion of times and (!) rates I would suggest to have: years (yr), quarter years (qtr), months (mo), and weeks (wk) available (next to d, h, min, s) , as these are all reasonable units of time depending upon the setting and they also reflect the choices a user has in most dedicated SD modeling software.

Note: The abbreviation "y" , which is by default already included in the unit conversion table, to me looks a lot less common - I would suggest to go for "yr" instead.

The convenient treatment of rates is (unfortunately) a matter I have not really solved yet: To my understanding, one would have to define a conversion for each and every rate possible, e.g. there needs to be different conversion for apples/second and oranges/second. Thus, working with seconds as the principal unit of time necessitates, in my opinion, that one drops all units for counting stocks in System Dynamics (e.g. money, people, equipment, factories, shops, etc.) so that we only need to convert dimensionless rates (e.g. 1/s)? -- I would be very happy to hear, that this understanding of mine were wrong, and I would greatly appreciate, if you could offer a better way to deal with rates.

Guido

But WSM as of Version 12.0 already ships with a predefined conversion:

The first entry is the predefined value and the second one is my custom entry. As you can see, assuming 365 days/year most often suffices.

Your doubts about a single, unchallenged definition for one year in seconds is of course very to the point (scientifically and technically) and they concisely illustrate the difficulties in adapting Modelica/WSM to the more abstract and diffuse requirements of business and social sciences modeling.

Very often, e.g. in strategic business modeling, we will have much more important uncertainties to worry about than imprecise definitions for a "year". If accuracy really matters, then we should indeed go back to days. Most data we get are concerned with some kind of period average and even then other factors matter (e.g. revenue as a function of business days not days in a calendar year; a leap year might have actually less business days than a regular year...).

Ultimately, you are imo making a case for leaving it all up to the modeler and the model's user to judge for themselves what they need in a given context:

Indeed agood case in point for allowing to have a custom conversion table that can easily be applied to modify the display of the system time.

Guido

Hello Guido,

We have had some discussions and we think we possibly could implement some automatic support for handling conversion of rates. We have considered a scenario where you have a variable with unit "apples/s" and a displayUnit "apples/year". Given that you have a conversion "1/s" to "1/year" the conversion for "apples/s" to "apples/year" would automatically be inferred. Would that be what you want?

Carl,

Actually, the choice in the GenericWithX case would be nested like this:

1. Time or not Time? (If Time then unit = "s" /* choice ends here */ else NestedChoice 2)
2. Rate or Not Rate? (In both cases determine base unit (e.g. replacement for "1"); If Rate then add "/s" to the base unit)

Something like this would be helpful.

I am hoping for some of the functionality mentioned by you and Otto being added soon and thus I will go for "seconds" in time and rates. ;-)

Note: That setting up an experiment (e.g. start time and stop time) for a simulation that goes from start time = 2010 [yr] to 2030 [yr] in seconds is PITA. One also has to be very disciplined in setting up TimeTables (e.g. start values with 0 or an actual date).

Guido