====== Tutorial 8 - Editing the function ======

===== 3/4 =====



The function editing window has three tabs:

  * **Properties** - This tab lets you define the name of the function, and also lets you (optionally) describe the function parameters.
  * **Source** - Where the function code is written.
  * **Libraries** - Allows you to add dependent libraries and source files.

  - Make sure that the **Properties** tab is selected.
  - Enter the name “my_add” for the function.
  - Select the “Source” tab.

The source page has a text box where you enter the source code for the function. A source template is automatically created for you, and is displayed in the text box. The areas in grey are not editable.

The function method takes a [[http://en.wikipedia.org/wiki/Variadic_function#Variadic_functions_in_C.23.2C_VB.net.2C_and_Java|varargs]] parameter named “params”. When the function is called from Ecolego, all the function arguments are stored in this variable.

For instance, consider an equation in Ecolego specifying “Comp1*my_function(A,B)”, where A and B are objects in your model. The values of A and B, at the time the function is called, will now be packaged into an [[http://simple.wikipedia.org/wiki/Array|array]], so that

params[0] = A\\
params[1] = B

The function ends with a “return Double.NaN” statement. You should here replace Double.NaN with the return value of your function.

  - Replace the text inside the white part of the text box with the following rows:

<code>

    double a=params[0];
    double b=params[1];

    return a+b;

</code>
  - Click on the **Test** button to make sure that the source code is valid.
  - Click ok to finalize editing of the function.


**Next**
  * [[Tutorial_8-Using_the_function|Using the function (4/4)]]

**Previous**
  * [[Tutorial_8-Creating_the_function|Creating the function (2/4)]]

**References**

  * [[Tutorials|Back to Tutorials]]
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