====== Transport begin ======

The transport begin represents the first compartment in a transport sub-system, and is “duplicated” when the simulation starts so that the total number of compartments (including the [[Transport_end|end]] compartment) equals [[Transport_N|N]]. This has the effect that the initial condition of the begin block will be assigned to all compartments of the [[Transport|transport]].

The [[Transport_begin|begin]] block is automatically added when a [[Transport|transport]] sub-system is created. A [[Transport|transport]] sub-system can only contain one [[Transport_begin|begin]] block.

===== Editing the begin block =====

|Note|Most block properties can be edited directly in the [[Blocks_window|blocks window]].|

The block editor is shown by right-clicking the block in a window and selecting **Edit**. In the [[Blocks_window|Blocks window]], you can also show the block editor by selecting the block and clicking the {{:Edit24.png|Edit}} button, or by double-clicking the right-most “validation” column of the block.

The block editor has three tabs:

==== Properties ====

This page lets you edit basic properties such as name, sub-system and base unit. See [[Editing_properties|editing properties]] for more information.

==== Appearance ====

This page lets you edit the visual properties of the block in the [[Matrix_window|Matrix window]]. See [[Editing_appearance|Editing appearance]] for more information.

==== Values ====

This page lets you specify dimension and index specific properties.

**Dimension** - You can specify the dimension of the block by using the **Type** drop down list. Depending on the dimension the index drop down lists are activated. Note that compartments can only be either scalar or vector.

**Data** - The table let you specify index specific properties like initial conditions. Note that properties assigned here will be used for every compartment in the transfer sub-system.

  * **//Indices//** - For blocks that are non-scalar, the first columns will specify indices from the [[Index_list|index lists]]. This allows you to specify different expressions for different indices. The top row is named “default” and can be used when the same value should be set for all indices.
  * **Initial Condition** - Allows you to enter an expression for the initial inventory of the corresponding material. Note that a value, a parameter or an [[Expression|Expression]] in the initial condition is evaluated when the simulation is started and time = t0. The [[Expression_editing_tool|Expression editing tool]] is available to help the user to enter and edit data.
  * **dy/dt** - Lets you add extra term to the differential equation of the compartment. This feature is useful, for instance, for a simple integration of values where it is not logical to modify the state of the compartment through transfers.
  * **Non-negative** – If set, the inventory of the compartment cannot be negative. //Default = “disabled”//
  * **Abs. error tol.**– Sets the absolute error tolerance for the given material. If empty, the “global” value set in simulation settings is used. //Default = ''%%<empty>%%''//
  * **Information** - By using the [[Table_control_button|Table control button]] you can display more columns that will help you document your model.

===== See also =====

  * [[Transport|Transport]]
  * [[Block|Blocks]]
  * The [[Matrix_window|Matrix window]]