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Model

Signal-Flow Approach in Modelling

Causal adopts signal-flow approach in systems modelling. In signal-flow approach, a Model consists of connected components. The components are data processing units and the behavior, i.e, the mathematical model, of the component determines how the data is processed. Connections connects the components each other and the data is transferred between components by means of connections. The data flow through the connections is unidirectional, i.e., a component is driven by other components that write data to its input bus.

Construction of Models

A Model consists of connected components. The components of are defined first and the Model consisting of these components can be constructed. Or, an empty model can be constructed.

Let us continue with some examples. We will construct very simple Model consisting of a SinewaveGenerator and a Writer. We construct an empty Model first, then we add nodes and branches as desired.

julia> using Causal # hide

julia> model = Model()
Model(numnodes:0, numedges:0)

julia> addnode!(model, SinewaveGenerator(), label=:gen)
Node(component:SinewaveGenerator(amp:1.0, freq:1.0, phase:0.0, offset:0.0, delay:0.0), idx:1, label:gen)

julia> addnode!(model, Writer(Inport()), label=:writer)
ERROR: MethodError: no method matching Writer(::Inport{Inpin{Float64}})
Closest candidates are:
  Writer(::A, !Matched::String, !Matched::FL, !Matched::var"##253", !Matched::var"##254", !Matched::var"##255", !Matched::Symbol, !Matched::var"##256", !Matched::var"##263", !Matched::Int, !Matched::var"##264", !Matched::var"##265", !Matched::var"##266", !Matched::var"##267") where {A, FL, var"##253", var"##254", var"##255", Symbol, var"##256", var"##263", Int, var"##264", var"##265", var"##266", var"##267"} at /home/runner/work/Causal.jl/Causal.jl/src/components/sinks/sinks.jl:122
  Writer(; action, path, f, file, trigger, handshake, callbacks, name, id, input, buflen, plugin, timebuf, databuf, sinkcallback) at util.jl:448

julia> addbranch!(model, :gen => :writer, 1 => 1)
ERROR: BoundsError: attempt to access 0-element Array{Any,1} at index [1]

Simulation of Models

A Model to to be simulated consists of components connected to each other an a time reference.

julia> model.nodes         # Model components
1-element Array{Any,1}:
 Node(component:SinewaveGenerator(amp:1.0, freq:1.0, phase:0.0, offset:0.0, delay:0.0), idx:1, label:gen)

julia> model.branches      # Model components
Any[]

julia> model.clock         # Model time reference
ERROR: type Model has no field clock

The time reference is used to sample the continuous time signals flowing through the busses of the model and to rigger the components. The simulation is performed by triggering the components with the pulses generated by the time reference at simulation sampling time intervals. Having been triggered, the components evolve themselves, compute their outputs and writes them to their outputs.

Simulation Stages

Inspection

The inspection stage is the first stage of the simulation process. In this stag,e the model is first inspected in terms of whether it is ready for simulation. This inspection is carried out to see whether the model has some inconsistencies such as unterminated busses or presence of algebraic loops. If the model has unterminated busses, the data that is supposed to flow those unterminated busses cannot flow through those busses and the simulation gets stuck. An algebraic is the subset of model components whose output depends directly on their inputs. In such a case, none of the components can produce outputs to break the loop which leads again the obstruction of simulation. Thus, to continue the simulation, the model must not contain any of those inconsistencies. The model inspection is done with inspect! function.

Initialization

If the inspection stage results positive, the initialization stage comes next. In this stage, the tasks required for the busses of the model to be both readable and writable are activated and bound the busses. To this end, a reader and writer task are activated and bound to both sides of each bus. To initialize the model, initialize! function is used.

When the model is initialized, the pairs of components and component tasks are recorded into the task manager of the model. During the rest of the simulation, task manager keeps track of the tasks. Any exception or error that is thrown during the run stage of the simulation can be observed by means of the task manager of the model.

Run

The run stage follows the initialization stage. The tasks activated in the initialization stage wait for the components to be triggered by the model time reference. During the run stage, time reference, that is the model clock, triggers the components by writing pulses that are generated in the intervals of the sampling period of the simulation to their trigger links. The job defined in a task is to read input dat a from the its input bus, to calculate its next state, if any, and output, and write its calculated output to its output bus. The run stage, starts at the initial time of the time reference and continues until the end time of the time reference. run! function is used to run the models,

Termination

After the run stage, the tasks opened in the initialization stage are closed and the simulation is terminated. terminate! function is used to terminate the model

Models are constructed to simulate! them. During the simulation, components of the Model process data and the data is transferred between the components via connection. Thus, to simulate the Models, the components must be connected. In our model, the writer is used to record the output of gen. Thus, the flows from gen to writer. Thus, we connect gen output to writer input.

Note

During the Model construction, the order of addition of nodes to the model is not important. The nodes can be given in any order.

Full API

Causal.Branch — Type
struct Branch{NP, IP, LN<:(AbstractArray{var"#s301",1} where var"#s301"<:Link)}

Constructs a Branch connecting the first and second element of nodepair with links. indexpair determines the subindices by which the elements of nodepair are connected.

Fields

  • nodepair::Any

    Node pair connected by the branch

  • indexpair::Any

    Indices of output and input ports

  • links::AbstractArray{var"#s301",1} where var"#s301"<:Link

    Links of the branch

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Causal.Model — Type
struct Model{GR, ND, BR, TM, CB}

A Model consists of nodes and branches. Nodes are connected to each other through the branches. A Model instance is ready for simulation.

See also Node, Branch

Fields

!!! warning Models are units that can be simulated. As the data flows through the branches i.e. input output busses of the components, its is important that the components must be connected to each other. See also: simulate!

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Causal.Node — Type
struct Node{CP, L}

Constructs a model Node with component. idx is the index and label is label of Node.

Fields

  • component::Any

    Node component

  • idx::Int64

    Node index

  • label::Any

    Node label

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Causal.addbranch! — Function
addbranch!(model, nodepair)
addbranch!(model, nodepair, indexpair)

Adds branch to branched of model.

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Causal.addnode! — Method
addnode!(model, component; label)

Adds a node to model. Component is component and label is label the label of node. Returns added node.

Example

julia> model = Model()
Model(numnodes:0, numedges:0, timesettings=(0.0, 0.01, 1.0))

julia> addnode!(model, SinewaveGenerator(), label=:gen)
Node(component:SinewaveGenerator(amp:1.0, freq:1.0, phase:0.0, offset:0.0, delay:0.0), idx:1, label:gen)
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Causal.breakloop! — Function
breakloop!(model, loop)
breakloop!(model, loop, breakpoint)

Breaks the algebraic loop of model. The loop of the model is broken by inserting a Memory at the breakpoint of loop.

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Causal.clean! — Method
clean!(model)

Cleans the buffers of the links of the connections, internal buffers of components, current time of dynamical systems.

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Causal.deletebranch! — Method
deletebranch!(model::Model, branch::Branch)

Deletes branch from branched of model.

deletebranch!(model::Model, srcnode::Node, dstnode::Node)

Deletes branch between srcnode and dstnode of the model.

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Causal.getcomponent — Method
getcomponent(model, specifier)

Returns the component of model corresponding to specifier that can be either index or label of the component.

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Causal.getlinks — Method
getlinks(model, pair)

Returns the links of model corresponding to the pair which can be a pair of integers or symbols to specify the source and destination nodes of the branch.

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Causal.getnode — Method
getnode(model, idx::Int)

Returns node of model whose index is idx.

getnode(model, label)

Returns node of model whose label is label.

Example

julia> model = Model()
Model(numnodes:0, numedges:0, timesettings=(0.0, 0.01, 1.0))

julia> addnode!(model, SinewaveGenerator(), label=:gen)
Node(component:SinewaveGenerator(amp:1.0, freq:1.0, phase:0.0, offset:0.0, delay:0.0), idx:1, label:gen)

julia> addnode!(model, Gain(), label=:gain)
Node(component:Gain(gain:1.0, input:Inport(numpins:1, eltype:Inpin{Float64}), output:Outport(numpins:1, eltype:Outpin{Float64})), idx:2, label:gain)

julia> getnode(model, :gen)
Node(component:SinewaveGenerator(amp:1.0, freq:1.0, phase:0.0, offset:0.0, delay:0.0), idx:1, label:gen)

julia> getnode(model, 2)
Node(component:Gain(gain:1.0, input:Inport(numpins:1, eltype:Inpin{Float64}), output:Outport(numpins:1, eltype:Outpin{Float64})), idx:2, label:gain)
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Causal.initialize! — Method
initialize!(model, clock)

Initializes model by launching component task for each of the component of model. The pairs component and component tasks are recordedin the task manager of the model. The model clock is set! and the files of Writer are openned.

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Causal.inspect! — Function
inspect!(model)
inspect!(model, breakpoints)

Inspects the model. If model has some inconsistencies such as including algebraic loops or unterminated busses and error is thrown.

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Causal.run! — Function
run!(model, clock)
run!(model, clock, withbar)

Runs the model by triggering the components of the model. This triggering is done by generating clock tick using the model clock model.clock. Triggering starts with initial time of model clock, goes on with a step size of the sampling period of the model clock, and finishes at the finishing time of the model clock. If withbar is true, a progress bar indicating the simulation status is displayed on the console.

Warning

The model must first be initialized to be run. See also: initialize!.

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Causal.signalflow — Method
signalflow(model, args; kwargs...)

Plots the signal flow of model. args and kwargs are passed into gplot function.

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Causal.simulate! — Method
simulate!(model, clock; simdir, simprefix, simname, logtofile, loglevel, reportsim, withbar, breakpoints)

Simulates model. simdir is the path of the directory into which simulation files are saved. simprefix is the prefix of the simulation name simname. If logtofile is true, a log file for the simulation is constructed. loglevel determines the logging level. If reportsim is true, model components are saved into files. If withbar is true, a progress bar indicating the simualation status is displayed on the console.

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Causal.simulate! — Method
simulate!(model, ti, dt, tf; kwargs...)

Simulates the model starting from the initial time t0 until the final time tf with the sampling interval of tf. For kwargs are

  • logtofile::Bool: If true, a log file is contructed logging each step of the simulation.
  • reportsim::Bool: If true, model components are written files after the simulation. When this file is read back, the model components can be consructed back with their status at the end of the simulation.
  • simdir::String: The path of the directory in which simulation file are recorded.
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Causal.terminate! — Method
terminate!(model)

Terminates model by terminating all the components of the model, i.e., the components tasks in the task manager of the model is terminated.

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Causal.troubleshoot — Method
troubleshoot(model)

Prints the exceptions of the tasks that are failed during the simulation of model.

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Causal.@defmodel — Macro
@defmodel name ex

Construts a model. The expected syntax is. 

    @defmodel mymodel begin 
        @nodes begin 
            label1 = Component1()
            label2 = Component1()
                ⋮
        end
        @branches begin 
            src1 => dst1 
            src2 => dst2 
                ⋮
        end
    end

Here @nodes and @branches blocks adefine the nodes and branches of the model, respectively.

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