====Model screen====

The Model screen displays the mathematical model for the study and is in a sense the heart of the MERLIN-Expo software. It allows you to review all equations, parameters and variables of the model and to see how different parts of the model are related. 

This screen also lets you modify the model by replacing parts or adding new parts from the [[library]]. This way the mathematical model can be customized to fit your study. 

Two views are used to visualize the model, and you can switch between these using the {{ecolego16.png}} **Matrix** and {{graphview16.png}} **Graph** buttons. The [[#Matrix|matrix]] arranges the [[sub-system|sub-systems]] in the diagonal of a matrix with interactions displayed counter clock-wise in the off-diagonal elements. The [[#Graph|graph]] shows the [[sub-system|sub-systems]] as boxes connected with arrows. 

The **Information** button opens a browser in which [[:user_interface#information|information]] on the currently selected [[block|blocks]] is presented. 

====Toolbar====

| {{ help24.png }}| Help | Shows this page |

====Graph====

{{ :graph.png?direct&300|}} The classic way of visualizing models is by using boxes and arrows; a graph. The graph is displayed by clicking the **Graph** button.


===Moving and selecting===

Use the left mouse button to select a [[sub-system]] or an interaction (arrow). To select multiple [[sub-system|sub-systems]], keep the CTRL key pressed while clicking the [[sub-system|sub-systems]]. When a [[sub-system]] is selected, information about it is presented in the [[#information]] panel.  

You can move [[sub-system|sub-systems]] by keeping the left mouse button pressed and moving the mouse. 

[[Sub-system]] boxes will feature a small **+** button in the upper left corner. Clicking the **+** button will expand the box and show the contents within it. Collapse it by clicking the **-** button.

===Connecting sub-systems===

{{ ::graph_connecting.png?nolink|}}To connect [[sub-system|sub-systems]], move the mouse cursor to the center of the first [[sub-system]]. A green outline is displayed. Press the left mouse button and move the mouse cursor to the center of the second model. An arrow will now connect the first [[sub-system]] with the second model. 

Notes: 

  - MERLIN-Expo will often connect [[sub-system|sub-systems]] for you when you add them from the [[library]]. It is only in special situations that you need to create or edit the connections. 
  - Some [[sub-system|sub-systems]] cannot be connected, hence no green outline will appear.
  - To specify what is connected, you should [[#Editing|edit]] the connection.
  - The connection is one way. You might want to add a connection back from the second [[sub-system|sub-systems]] to the first. 

===Menu===

All action in the graph is accessed from the menu, which is displayed by clicking the right mouse button.

| {{edit24.png}} | Edit | [[#Editing|Edit]] the currently selected [[sub-system]] |
| | Add> | Quickly [[#Adding sub-systems|add]] a new [[sub-system]] to the [[model]] from the [[library]]. |
| | Get from library... | Add a new [[sub-system]] to the [[model]] from the library window. |
| |||
| | Sub-system | Creates a [[sub-system]]; a box with the only purpose of grouping [[sub-system|sub-systems]], much like a folder in a file system. If [[sub-system]] are selected when this button is pressed, they will all be moved to the new [[sub-system]]. |
| | Group | Creates a [[group]]. | 
| | Set background | Allows you to set the background for the [[model]] |
| | Toggle grid | Displays or hides a grid which simplify aligning [[sub-system|sub-systems]]. When a [[sub-system]] is moved it will snap to the grid. |
| {{print24.png}} | Print... | Print the graph |
| | Zoom > | |
| {{zoomin24.png}} |  Zoom In | Increase the size of the graph |
| {{zoomout24.png}} |  Zoom Out | Decrease the size of the graph |
| {{zoomselection24.png}} |  Restore Zoom | Restore the zoom to the original 100% |
| | Layout > | |
| |  Tree | Organise the [[sub-system|sub-systems]] as a tree |
| |  Organic | Organise the [[sub-system|sub-systems]] organically (with the most relevant [[sub-system|sub-systems]] in the center) |
| |  Hierarchical | Organise the [[sub-system|sub-systems]] in a hierarchy |
| |  Stack | Organise the [[sub-system|sub-systems]] in a (vertical) stack |
| | Navigate > | |
| |  Enter | Display the currently selected [[sub-system]] |
| |  Exit | Display the parent [[sub-system]] |
| |  Home | Display the top [[sub-system]] |


====Matrix====

{{ :matrix.png?direct&300|}} [[wp>Design_structure_matrix|Interaction matrics]] are useful for models with many interactions. [[sub-system|sub-systems]] are arranged diagonally, with interactions in the off-diagonal cells. This arrangement guarantees that off-diagonal cells never overlap and is great for smaller models with many interactions. However, for models with many [[sub-system|sub-systems]] but few interactions, the matrix tend to become very big and somewhat clumsy to work with. The interaction matrix is displayed by clicking the **Matrix** button.

===Moving and selecting===

Use the left mouse button to select a [[sub-system]] or an interaction. When more than four interactions are displayed in the same cell, click the {{more16.png}} button to show all the interactions. To select multiple [[sub-system|sub-systems]], keep the CTRL key pressed while clicking the [[sub-system|sub-systems]]. 

You can move [[sub-system|sub-systems]] by keeping the left mouse button pressed and moving the mouse. Press the {{expand16.png}} button to open a sub-system and {{collapse16.png}} to close it. 

===Connecting sub-systems===

{{ ::matrix_connecting.png?nolink|}}To connect models, move the mouse cursor to the same row as the first model and to the same column as the second model. Right-click an select **Connector** from the menu. 

Notes: 
  - MERLIN-Expo will often connect [[sub-system|sub-systems]] for you when you add them from the [[library]]. It is only in special situations that you need to create or edit the connections. 
  - To specify what is connected, you should [[#Editing|edit]] the connection.
  - The connection is one way. You might want to add a connection back from the second model to the first. 

===Menu===

The menu of the interaction matrix will vary depending on the context (or location) in which it is presented. For instance, if you click an off-diagonal cell then buttons related to the diagonal cells only will be hidden. 

| {{edit24.png}} | Edit... | [[#Editing|Edit]] the currently selected [[sub-system]] or interaction |
| | Connector (off-diagonal) | If an off-diagonal cell is selected, and the source and target models can be connected, creates a [[connector]] from the first to the second model. | 
| | Sub-system (diagonal cells) | Creates a [[sub-system]]. If [[sub-system|sub-systems]] are selected when this button is pressed, they will all be moved to the new sub-system. |
| | Group (diagonal cells) | Creates a [[group]]. | 
| | Add> (diagonal cells) | Quickly [[#Adding sub-systems|add]] a new [[sub-system]] to the model from the library. |
| | Get from library... (diagonal cells) | Add a new [[sub-system]] to the model from the library window. |
| | Insert above (diagonal cells) | Adds an empty cell above the currently selected cell (or to the top if no cell is selected) | 
| | Insert below (diagonal cells) | Adds an empty cell below the currently selected cell (or to the bottom if no cell is selected) | 
| |||
| {{delete24.png}} | Delete | Removes the currently selected [[sub-system]] or interaction |
| {{zoomin24.png}} | Zoom In | Increase the size of the matrix |
| {{zoomout24.png}} | Zoom Out | Decrease the size of the matrix |
| {{zoomselection24.png}} | Restore Zoom | Restore the zoom to the original 100% |

====Editing====

===Sub-systems===
The visual properties of a [[sub-system]] can be changed by right-clicking the object and choosing **Edit** from the menu. The window which appears has four tabs (sub-systems):

==Properties==
    
**Name** - Change the (short) name of the [[sub-system]]. This name lets you identify the object in the simulation results, and is also used to refer to the [[sub-system]] in equations.

==Appearance==
  * **General**
    * **Display name** - The label of the object.
    * **Font** - The font for the label
    * **Color** - The background color 
    * **Background color used** - Whether the background color is used or not. It is usually unnecessary to display a background color if an image is used (see below).
    * **Image** - Select an image to be used as the background. 
    * **Image shown** - Whether the image is shown or not.
  * **Matrix**
    * **Visible** - Displayed on the interaction matrix
  * **Graph**
    * **Visible** - Displayed on the graph
    * **Shape** - Draw a (geometric) shape for the object
    * **Glass effect** - Draw a graphic glass effect for the object
    * **Background image** - Select a background to be displayed behind the [[sub-system|sub-systems]] of a sub-system
    * **Background shown** - - Whether the background image is used or not.

==Inputs & Outputs==

These two tabs lets you select which objects of a sub-system that should be possible to connect to other sub-systems. You make an object available by selecting it in the left-hand list and clicking the >> arrow. 

Once selected, you can specify if it should allow more than one connection to another output/input. 

Notes:

  * It is unwise to change the pre-defined [[model input|inputs]] and/or [[model output|outputs]], as these are required for the tool to function normally. 

===Connections===

{{ ::edit_connector.png?nolink|}} An arrow which connects two [[sub-system|sub-systems]] is called a [[connector]]. It allows one sub-system to provide another sub-system with input data. When you right-click the arrow and choose **Edit**, a window appears which allows you to specify what data should be given to the target sub-system. 

The window contains a table with three columns. The center column lists all [[model input|inputs]] in the target sub-system. These are the data that the target sub-system asks for. By clicking the cells in the first column, you can select what data (which [[model output|output]]) from the source sub-system should be given to the target. In the picture you can see a connector between an atmosphere model sub-system and a fruit model sub-system. The fruit model needs data for dry deposition. When clicking in the cell next to **Surface dry deposition...** a menu appears which lists the data offered by the atmosphere model. Only data which is still accessible (some data can only be used by one sub-system) and which has the correct unit is displayed in the menu.

===Adding=== 

You can add new [[sub-system|sub-systems]] from the [[library]] to your model in two ways, both accessed from the right-click menu of the [[#graph]] or [[#matrix]].

  * **Get from library...** - Select a model [[sub-system]] from the library window. This window lets you read the description of the model before you add it.
  * **Add >** - If you already know which model you want to add, you can quickly add the model from this button. Moving the mouse cursor will produce a sub-menu from which you can select a model.

If there are already model [[sub-system|sub-systems]] in the project when a model is added, the software will ask if you want to automatically connect the new model [[sub-system]] with the existing [[sub-system|sub-systems]].