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ERT 355/2: BIOSYSTEMS MODELLING AND SIMULATIONS LAB MODULE – LABVIEW (WEEK 9)

PREPARED BY KHAIRUL RABANI

UNIVERSITY OF MALAYSIA PERLIS SCHOOL OF BIOPROCESS ENGINEERING

(BIOSYSTEMS ENGINEERING) SEMESTER 2 2015/2016

ERT 355 / 2 BIOSYSTEMS MODELLING AND DESIGN

LABORATORY MODULE - LABVIEW

WEEK 9

“ARRAY”

“FORMULA NODES”



Chapter Outline

Chapter 3: Array ................................................................................................. 3

Tutorial 3.1: Creating Array Controls and Indicators..................................... 3

Tutorial 3.2: Creating Array Constants .......................................................... 7

Tutorial 3.3: Array Inputs/Outputs ................................................................. 8

Tutorial 3.4: Matrix ....................................................................................... 12

EXERCISE 1 ................................................................................................ 15

Chapter 4: Formula Nodes ............................................................................... 16

Tutorial 4.1: Using the Formula Node .......................................................... 17

Resources ................................................................................................... 21

Tutorial 4.2: Using the MathScript Node ..................................................... 21



Chapter 3: Array

An array, which consists of elements and dimensions, is either a control or an

indicator – it cannot contain a mixture of controls and indicators. Elements are the data or

values contained in the array. A dimension is the length, height, or depth of an array.

Arrays are very helpful when you are working with a collection of similar data and when

you want to store a history of repetitive computations.

Array elements are ordered. Each element in an array has a corresponding index

value, and you can use the array index to access a specific element in that array. In NI

LabVIEW software, the array index is zero-based. This means that if a one-dimensional

(1D) array contains n elements, the index range is from 0 to n – 1, where index 0 points to

the first element in the array and index n – 1 points to the last element in the array.

Tutorial 3.1: Creating Array Controls and Indicators

To create an array in LabVIEW, you must place an array shell on the front panel and then

place an element, such as a numeric, Boolean, or waveform control or indicator, inside the

array shell.

1. Create a new VI.

2. Right-click on the front panel to display the Controls palette.

3. On the Controls palette, navigate to Modern»Array, Matrix, & Cluster and drag

the Array shell onto the front panel.



4. On the Controls palette, navigate to Modern»Numeric and drag and drop a

numeric indicator inside the Array shell.

5. Place your mouse over the array and drag the right side of the array to expand it and

display multiple elements.



The previous steps walked you through creating a 1D array. A 2D array stores elements in

a grid or matrix. Each element in a 2D array has two corresponding index values, a row

index and a column index. Again, as with a 1D array, the row and column indices of a 2D

array are zero-based.

To create a 2D array, you must first create a 1D array and then add a dimension to it.

Return to the 1D array you created earlier.

1. On the front panel, right-click the index display and select Add Dimension from

the shortcut menu.



2. Place your mouse over the array and drag the corner of the array to expand it and

display multiple rows and columns.

Up to this point, the numeric elements of the arrays you have created have been dimmed

zeros. A dimmed array element indicates that the element is uninitialized. To initialize an

element, click inside the element and replace the dimmed 0 with a number of your choice.

You can initialize elements to whatever value you choose. They do not have to be the same

values as those shown above.



Tutorial 3.2: Creating Array Constants

You can use array constants to store constant data or as a basis for comparison with another

array.

1. On the block diagram, right-click to display the Functions palette.

2. On the Functions palette, navigate to Programming»Array and drag the Array

Constant onto the block diagram.

3. On the Functions palette, navigate to Programming»Numeric and drag and drop

the Numeric Constant inside the Array Constant shell.



4. Resize the array constant and initialize a few of the elements.

Tutorial 3.3: Array Inputs/Outputs

If you wire an array as an input to a for loop, LabVIEW provides the option to

automatically set the count terminal of the for loop to the size of the array using the Auto-

Indexing feature. You can enable or disable the Auto-Indexing option by right-clicking the

loop tunnel wired to the array and selecting Enable Indexing (Disable Indexing).

If you enable Auto-Indexing, each iteration of the for loop is passed the corresponding

element of the array.

When you wire a value as the output of a for loop, enabling Auto-Indexing outputs an

array. The array is equal in size to the number of iterations executed by the for loop and

contains the output values of the for loop.

1. Create a new VI. Navigate to File»New VI.

2. Create and initialize two 1D array constants, containing six numeric elements, on

the block diagram similar to the array constants shown below.



3. Create a 1D array of numeric indicators on the front panel. Change the numeric

type to a 32-bit integer. Right-click on the array and select Representation»I32.

4. Create a for loop on the block diagram and place an add function inside the for

loop.

5. Wire one of the array constants into the for loop and connect it to the x terminal of

the add function.



6. Wire the other array constant into the for loop and connect it to the y terminal of

the add function.

7. Wire the output terminal of the add function outside the for loop and connect it to

the input terminal of the array of numeric indicators.

8. Your final block diagram and front panel should be similar to those shown below.

Block Diagram



Front Panel

9. Go to the front panel and run the VI. Note that each element in the array of

numeric indicators is populated with the sum of the corresponding elements in the

two array constants.

Be aware that if you enable Auto-Indexing on more than one loop tunnel and wire the for

loop count terminal, the number of iterations is equal to the smaller of the choices. For

example, in the figure below, the for loop count terminal is set to run 15 iterations, Array 1

contains 10 elements, and Array 2 contains 20 elements. If you run the VI in the figure

below, the for loop executes 10 times and Array Result contains 10 elements. Try this and

see it for yourself.



You can create a 2D array using nested for loops and Auto-Indexing as shown below. The

outer for loop creates the row elements, and the inner for loop creates the column elements.

Tutorial 3.4: Matrix

Use the matrix data type instead of a 2D array to represent matrix data because the

matrix data type stores rows or columns of real or complex scalar data for matrix

operations, particularly some linear algebra operations. The Mathematics VIs that perform

matrix operations accept the matrix data type and return matrix results, which enables

subsequent polymorphic VIs and functions in the data flow to perform matrix-specific

operations. If a Mathematics VI does not perform matrix operations but accepts a matrix

data type, the VI automatically converts the matrix data type to a 2D array. If you wire a



2D array to a VI that performs matrix operations by default, the VI automatically converts

the 2D array to a real or complex matrix, depending on the data type of the 2D array.

1. Create a new VI. Navigate to File»New VI.

2. On the Functions palette, navigate to Modern»Array,Matrix&Cluster and drag

the RealMatrix onto front panel.

3. Fill each element in the matrix of numeric indicators as shown below and rename

as Matrix A.



4. Create a second matrix by repeat step 2 and 3. Fill each element of the matrix and

rename as Matrix B as shown below.

5. Wire the Matrix A and B to the x and y terminals of the add function.

6. Create indicator at output terminal of the add function.

7. Go to the front panel and run the VI.



EXERCISE 1

1. Repeat Tutorial 3.4 by subtracts, multiply and divides the matrixes by using single

case selection VI.

2. Solving systems of linear equations is one of the most common computations in

science and engineering, and is easily handled by LabVIEW. Consider the following

set of linear equations. 5x = 3y − 2z + 10 8y + 4z = 3x + 20 2x + 4y − 9z = 9. This set

of equations can be re-arranged so that all the unknown quantities are on the left-

hand side and the known quantities are on the right-hand side.

5x − 3y + 2z = 10

−3x + 8y + 4z = 20

2x + 4y − 9z = 9



Chapter 4: Formula Nodes

A Formula Node is a box where you enter algebraic formulas directly into the

Block Diagram. The Formula Node in the LabVIEW software is a convenient, text-based

node you can use to perform complicated mathematical operations on a block diagram

using the C++ syntax structure. It is most useful for equations that have many variables or

are otherwise complicated. The text-based code simplifies the block diagram and increases

its readability. Furthermore, you can copy and paste existing code directly into the Formula

Node rather than recreating it graphically.

In addition to text-based equation expressions, the Formula Node can accept text-

based versions of if statements, while loops, for loops, and do loops, which are familiar to

C programmers. These programming elements are similar but not identical to those you

find in C programming.

The MathScript Node implements similar functions but with the additional

functionality of a full .m file compiler, making it useful as a textual language for signal

processing, analysis, and math. LabVIEW MathScript is generally compatible with .m file

script syntax, which is widely used by alternative technical computing software. For

LabVIEW 2009 and later, the LabVIEW MathScript features are released separately in the

LabVIEW MathScript RT Module.



It is useful when an equation is complicated or has many variables. Below is an example of

how you would implement y = x^2 + x + 1 with regular block diagram nodes:

It is much easier to use the Formula Node. Below is an example:

Tutorial 4.1: Using the Formula Node

Complete the following steps to create a VI that computes different formulas depending on

whether the product of the inputs is positive or negative.

1. Selecting File»New VI to open a blank VI.

2. Place a Formula Node on the block diagram.

1. Right-click on the diagram and navigate to Programming»Structures»Formula

Node.

2. Click and drag the cursor to place the Formula Node on the block diagram.



3. Right-click the border of the Formula Node and select Add Input from the shortcut

menu.

4. Label the input variable x.

5. Repeat steps 3 and 4 to add another input and label it y.

6. Right-click the border of the Formula Node and select Add Output from the shortcut

menu.



7. Create two outputs and name them z1 and z2, respectively.

Note: It is considered good programming practice to keep the inputs on the left border and

the outputs on the right border of the Formula Node. This helps you follow the data flow in

your VI and keep your code organized.

8. Enter the expressions below in the Formula Node. Make sure that you complete each

command with a semicolon. Notice, however, that the if statement does not require a

semicolon after the first line.

if (x*y>0)

z1 = 3*x**2 - 2*y**3;

else z1 = 0;

z2 = sinh(z1);

9. Create controls and indicators for the inputs and outputs.

1. Right-click on each input and select Create»Control from the shortcut menu.



2. Right-click on each output and select Create»Indicator from the shortcut menu.

10. Place a While Loop with a stop button around the Formula Node and the controls. Be

sure to include a Wait (ms) function inside the loop to conserve memory usage. Your

block diagram should appear as follows.

11. Click the Run button to run the VI. Change the values of the input controls to see how

the outputs change.

In this case, the Formula Node helps minimize the space required on the block diagram.

Accomplishing the same task without the use of a Formula Node requires the following

code.



Resources

For more information on the Formula Node syntax or the functions available, see the

LabVIEW Help by pressing the <Ctrl-H> keys while you are developing your code. This

opens the Context Help window, which includes information about the feature that your

mouse is hovering over. In the Context Help window, select Detailed help for more

information.

Tutorial 4.2: Using the MathScript Node

Complete the following steps to create a VI that performs various operations on a 1D array

in LabVIEW.

1. Open a blank VI from the toolbar by selecting File»New VI.

2. Place a MathScript Node on the block diagram.

1. Right-click on the diagram and navigate to

Programming»Structures»MathScript Node.

http://zone.ni.com/reference/en-XX/help/371361D-01/glang/formula_node/



2. Click and drag the cursor to place the MathScript Node on the block diagram.

3. In the same manner as you implemented in the Formula Node exercise, right-click on

the border and select Add Input from the shortcut menu. Label the input x.

4. Right-click the border and select Add Output from the shortcut menu. Repeat this

process to create three outputs labeled y, y1, and d. For LabVIEW 2010 and later select

Add Output»Undetected Variable.

5. Place an array of numeric controls on the front panel. Label the array x and wire it to

the x input of the MathScript Node on the block diagram.

6. In the MathScript Node, enter the following expressions:

y = x.^2;

y1 = y(1);

d = dot(x,y);

7. Create indicators for each of the three outputs by right-clicking each output and

selecting Create»Indicator from the shortcut menu.

8. Place a While Loop with a stop button around the MathScript Node and the controls.

Be sure to include a Wait (ms) function inside the loop to conserve memory usage.

Your block diagram should appear as follows.



9. On the front panel, expand the arrays to show multiple elements. With the cursor, grab

the bottom middle selector of the array and drag it down to show multiple elements.

10. Begin by placing a 1, 2, and 3 in the first three elements of the x control. Your front

panel should look similar to the one below. Note that the fourth and fifth elements are

grayed out. This is because they are not initialized. You can initialize them by clicking

inside the cell and entering a value. To uninitialize a cell, right-click the element and

select Data Operations»Delete Element from the shortcut menu.



11. Click the Run button. Change the values of the elements in the array to see how the

outputs change.

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