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## Create a Simple Model

### Model Overview for This Tutorial

You can use Simulink® to model a system and then simulate the dynamic behavior of that system. The basic techniques you use to create a simple model in this tutorial are the same techniques that you use for more complex models.

To create this simple model, you need four blocks:

• Sine Wave — Generates an input signal for the model.

• Integrator — Processes the input signal.

• Bus Creator — Combines the input signal and processed signal into one signal.

• Scope — Visualizes the signals.

Simulating this model integrates a sine wave signal to a cosine signal and then displays the result, along with the original signal, in a scope window.

### Open the Simulink Library Browser

From the Simulink Library Browser, you can create a new model (block diagram) and search for blocks that you want to use in your model. You need MATLAB® running before you can open the Simulink Library Browser.

1. From the MATLAB Toolstrip, click the Simulink Library button , or in the Command Window, enter

`      simulink`

A short delay occurs before the Simulink Library Browser opens.

2. In the Simulink Library Browser, select View > Stay on Top to keep the Library Browser on top of the other windows on your desktop.

### Browse or Search for Specific Blocks

To browse through the block libraries, select a MathWorks® product, and then select a functional area. Alternatively, you can search all of the available block libraries at once.

1. Browse for the block. In the Libraries pane on the left, select Simulink, and then select the Sources library. From the Library displayed in the right pane, select the Sine Wave block.

2. Search for a block. In the search box, enter a block name or part of a block name. For example, enter sine, and then click the Search button .

3. Get detailed information about a block. Select the block, and then from the menu bar, select Help > Help for the Selected Block. The Help browser opens with the reference page for that block.

4. View block parameters. Right-click a block, and then select Block Parameters. The block parameters dialog box opens.

### Open the Simulink Editor

In the Simulink Editor, you can build and simulate models of your system. You need the Simulink Library Browser open before you can create a new Simulink model.

1. From the Simulink Library Browser Toolstrip, click the New Model button , or from the menu bar, select File > New > Model.

A Simulink Editor window opens with an new block diagram in the right pane.

2. Select File > Save as. In the File name text box, enter a name for your model. For example, enter simple_model, and then click Save.

Simulink saves your model with the file name simple_model.slx.

### Add Blocks to a Model

To build a model, begin by copying blocks from the Simulink Library Browser to the Simulink Editor.

1. In the Simulink Library Browser, select the Sources library. The Library Browser displays blocks from the selected library in the right pane.

2. Select the Sine Wave block, and then drag the block to the block diagram.

A copy of the Sine Wave block appears in your model.

3. Add the following blocks to your model, using the same approach that you used to add the Sine Wave block.

LibraryBlock
SinksScope
ContinuousIntegrator
Signal RoutingBus Creator

Your model now has the blocks you need for the simple model.

### Move and Resize Blocks

Before you connect the blocks in your model, arrange them logically to make the signal connections as straightforward as possible.

1. Move the Scope block after the Bus block output. You can either:

• Click and drag a block.

• Select the block, and then press the arrow keys on your keyboard.

2. Move the Sine Wave and Integrator blocks before the Bus block.

Move the blocks until your model looks similar to the following figure.

### Simulink Block Connections

After you add blocks to your model, you need to connect them. The connecting lines represent the signals within your model.

Most blocks have angle brackets on one or both sides. These angle brackets represent input and output ports:

• The > symbol pointing into a block is an input port.

• The > symbol pointing out of a block is an output port.

### Draw Signal Lines Between Blocks

Connect the blocks by drawing lines between output ports and input ports.

1. Position the cursor over the output port on the right side of the Sine Wave block.

The pointer changes to a cross hair (+) while over the port.

2. Click, and then drag a line from the output port to the top input port of the Bus block.

While you are holding down the mouse button, the connecting line appears as a red dotted arrow.

3. Release the mouse button when the pointer is over the output port.

Simulink connects the blocks with a line and an arrow indicating the direction of signal flow.

4. Connect the output port of the Integrator block to the bottom input port on the Bus block using this alternative procedure:

1. Select the Integrator block.

2. Press and hold the Ctrl key.

3. Click the Bus block.

The Integrator block connects to the Bus block with a signal line.

 Note:   The Ctrl+click shortcut is useful when you are connecting widely separated blocks or when working with complex models.
5. Connect the Bus block output port to the Scope block.

### Draw Branched Signal Lines

Your simple model is almost complete. To finish the model, connect the Sine Wave block to the Integrator block.

This connection is different from the other connections, which all connect output ports to input ports. Because the output port of the Sine Wave block is already connected, you must connect this existing line to the input port of the Integrator block. The new line, called a branch line, carries the same signal that passes from the Sine Wave block to the Bus block.

1. Hold down the Ctrl key.

2. Position the cursor where you want to start a branch line. Click, and then drag the cursor away from the line to form a dotted-red line segment.

3. Drag the cursor to the Integrator input port, and then release the mouse button.

4. Drag line segments to straighten and align with blocks. Your model is now complete.

### Define Simulation Parameters

Before you simulate the behavior of a model, define the simulation parameters. Simulation parameters include the type of numerical solver, start and stop times, and maximum step size.

1. From the Simulink Editor menu, select Simulation > Model Configuration Parameters. The Configuration Parameters dialog box opens to the Solver pane.

2. In the Stop time field, enter 20. In the Max step size field, enter 0.2.

3. Click OK.

### Run Simulation

After you define Model Configuration Parameters, you are ready to simulate your model.

1. From the Simulink Editor menu bar, select Simulation > Run.

The simulation runs, and then stops when it reaches the stop time specified in the Model Configuration Parameters dialog box.

 Tip   Alternatively, you can control a simulation by clicking the Run simulation button and Pause simulation button on the Simulink Editor toolbar.

### Observe Simulation Results

After simulating a model you can view the simulation results in a Scope window.

1. Double-click the Scope block.

The Scope window opens and displays the simulation results. The plot shows a sine wave signal with the resulting cosine wave signal from the Integrator block.

2. From the Scope block toolbar, click the Parameters button . Select the Style tab. The Scope Parameters dialog box displays figure editing options.

3. Change the appearance of the figure. For example, select white for the Figure color and Axes background color (icons with a pitcher) and black for the Ticks, labels and grid colors (icon with a paintbrush). Change the signal line colors for signal 1 to blue and for signal 2 to green. To see your changes, click OK.

4. Select File > Close > Close Model. The Simulink Editor closes with changes to your model and the model configuration parameters.