It seems that it is at least not encouraged to write Modelica functions with connectors as arguments. I get a warning if I try it.
Assume I have a connector
connector con
Real x;
Real y;
end con;
a record
record rec
Real x;
Real y;
end rec;
and a function
function f
input rec r[:];
output Real z;
algorithm
...
end f;
Given an array of connectors, i.e. con c[N], how can I convert it into an array of records rec?
One approach would be to use a function
function convert
input Integer N;
input Real x[N];
input Real y[N];
output rec z[N];
algorithm
z.x := x;
z.y := y;
end convert;
and call it via convert(size(c, 1), c.x, c.y).
Is there a simpler way?
Related
I have a function that does or does not have a derivative and inverse, depending on values of some parameters/coefficients. Can I make the annotations derivative and inverse conditional somehow?
Something like
function y_from_x
input Real x;
input Boolean hasInverse;
output Real y;
...
equation
...
annotation(inverse(x=x_from_y(y=y) if hasInverse));
end y_from_x;
There is no direct support for that in the Modelica specification.
What you could do is something like:
function y_from_x
input Real x;
input Boolean hasInverse;
output Real y;
...
algorithm
y:=if hasInverse then y_from_x1(x) else y_from_x2(x);
annotation(Inline=true);
end y_from_x;
function y_from_x1
input Real x;
output Real y;
...
algorithm
y:=y_from_x2(x);
annotation(inverse(x=x_from_y(y=y)));
end y_from_x1;
function y_from_x2
input Real x;
output Real y;
...
algorithm
...
end y_from_x2;
In Modelica, I'm able to access the contents of a record instance like so:
model Unnamed1
record Example
parameter Real x = 5;
end Example;
Example ex;
Real test;
equation
test = ex.x;
end Unnamed1;
However, I'd like to access the contents of the record without declaring an instance of the record, like so:
model Unnamed1
record Example
parameter Real x = 5;
end Example;
Real test;
equation
test = Example().x;
end Unnamed1;
...but this doesn't work. Is there some way to achieve what I'm trying to do?
Yes, it is possible without having an actual instance in the model but it requires some extra code.
model Unnamed1
record Example
parameter Real x = 5;
end Example;
function getX
input Example r;
output Real x;
algorithm
x:=r.x;
end getX;
Real test;
equation
test = getX(Example());
end Unnamed1;
(I'm aware that it is cheating by having the instance in the function, but....)
Another option is
for r in {Example()} loop
test=r.x;
end for;
(allowed according to https://github.com/modelica/ModelicaSpecification/issues/1521 )
This is not possible (even from a grammar point of view). The right hand side of dot (.) needs to be a class or component reference. You can only access constants/parameters in packages via the dot notation.
package X
constant Real x = 1;
end X;
model M
Real x = X.x
end M;
The following three questions are tied together so please forgive the length of the post.
Using Dymola 2016.
Using a replaceable function call within a model provides the opportunity for the user to have the drop down options. Example below:
model Test1
parameter Real x = 1;
Real y;
replaceable function a=b constrainedby d annotation(choicesAllMatching=true);
equation
y = a(x);
end Test1;
Doing the same replaceable function call within a function seems to not permit the same drop down functionality with the the function is called (i.e. right click call function in package browser. I assume this is intentional as a function is typically called within other functions/models. Example below:
function Test2
input Real x;
output Real y;
replaceable function a=b constrainedby d annotation(choicesAllMatching=true);
algorithm
y :=a(x);
end Test2;
Question #1. Is it possible to use a replaceable function call within a function in the same way you do a model? If so, what is the appropriate syntax? Alternative approach?
Alternatively, a different option would be to perform the replaceable function call in the model and then pass the result to another function that then makes the appropriate call. Example shown below:
model Test3mod
parameter Real x = 1;
Real y;
replaceable function a=b constrainedby d annotation(choicesAllMatching=true);
equation
y = Test3func(x,a);
end Test3mod;
Which passes parameter x and function handle a to:
function Test3func
input Real x;
input ???? a;
output Real y;
algorithm
y :=a(x);
end Test3func;
Question #2. Is this allowable in Modelica and if so, how? Alternative approach?
Question #3. Is it possible to define a string and turn that into a the name of a function. Example below:
model Test4
parameter String 'functionname';
parameter Real x = 1;
Real y;
equation
y = functionname(x);
end Test4;
Thank you in advance! I appreciate your feedback as I continue to explore the use of Modelica.
This should work fine:
model Test3mod
parameter Real x = 1;
Real y;
replaceable function a=b constrainedby d annotation(choicesAllMatching=true);
equation
y = Test3Func(x,a);
end blah;
function Test3func
input Real x;
input d f;
output Real y;
algorithm
y := f(x);
end Test3func;
I would like to use a class function/method in my Modelica model as follows:
optimization Moo(objective=-x(finalTime), startTime = 0, finalTime = 12)
parameter Real e = 0.05;
Real x(start=2, fixed=true, min=0, max=100);
input Real v (min=0, max=1);
function omega
input Real t;
output Real y;
algorithm
y := e;
end omega;
equation
der(x) = v*omega(time);
constraint
v<=1;
end Moo;
I would like the variable e in the function omega to be a variable so that I can easily change its value at a later point in time when I am doing a parameter sweep. Unfortunately, the function omega does not seem to know about the variable e and the JModelica compiler returns the error:
Cannot find class or component declaration for e
I would naïvely expect that since omega and e belong to the same class omega would be able to see e.
Is there a way to achieve this?
Member functions are not supported in Modelica, so a function declared inside a model acts like a standalone function without having access to the surrounding model variables.
Member functions are not allowed due to functions need to be pure, i.e. they are not allowed to have any side effect. This is a fundamental assumption in Modelica that makes it possible for a tool to apply symbolic transformation and rearrange calculations.
You can have something like a member function, if you explicitly pass the needed variables as additional input to the function. See this example:
package MemberFunction
model A
Real x=1;
function get_x = MemberFunction.get(u=x);
end A;
function get
input Real u;
output Real y;
algorithm
y := u;
end get;
model Test
A a;
Real x;
equation
x = a.get_x();
end Test;
end MemberFunction;
Assume I have a large connector involving all kinds of base types (Real, Integer, String, Boolean). How can I switch connections based on state events?
I would like to do something like this:
model switch
input ComplicatedConnector icon[2];
output ComplicatedConnector ocon;
input Real x;
equation
if x >= 0 then
connect(ocon, icon[1]);
else
connect(ocon, icon[2]);
end if;
end switch;
This does not work. How can it be properly expressed in Modelica?
Answer based on comment by Adrian Pop.
model switch
input ComplicatedConnector icon[2];
output ComplicatedConnector ocon;
input Real x;
ComplicatedConnector con;
initial equation
con = icon[1];
equation
connect(ocon, con);
when x >= 0 then
con := icon[1];
end when;
when x < 0 then
con := icon[2];
end when;
end switch;
Update: The model above is wrong because ocon outputs the initial value of icon[1] forever if no event occurs which is not what you would expect from a switch. Note that this is not due to a wrong answer but due to my false interpretation of the answer. The following model is based on the answer by Michael Tiller.
model switch
input ComplicatedConnector icon[2];
output ComplicatedConnector ocon;
input Real x;
Integer k;
initial equation
k = 1;
equation
ocon = icon[k];
when x >= 0 then
k := 1;
elsewhen x < 0 then
k := 2;
end when;
end switch;
Is not possible. You can only switch them based on a parameter known at compile time (also known as structural parameter). The condition in the if equation containing connects needs to be a parameter expression.
Note that connect statements are equations. You can expand them out yourself. They exist mainly to avoid "bookkeeping" errors for generating boilerplate equations. So what I suggest you do is simply take your switch model and expand each connect into equations. The it should work.