Introduction to
LabVIEW MathScript

• In the Command window: Execute the following commands (by typing the text lines followed by the Enter button on the keyboard when at the end of each line):

  10+20 (Enter). Observe the result in the Output window.
  a=1;
  b=2;
  c=a+b
   

• Open the Variables window just to see the variables generated. Note that the scalars, as a, b, c etc., are displayed as 2 dimensional arrays (corresponding to a matrix in MATLAB).
• Open the History window to see the history of commands.

• Open a blank VI, save it as my_mathscript.vi in any folder you prefer.
• Add the following to the Front panel, as on the Front panel of mathscript_example:
  • Two Matrix controls from the Controls / Array & Matrix palette, and label them A (real matrix) and x (real matrix), respectively.
  • One Matrix indicator from the Controls / Array & Matrix palette, and label it y (real matrix).
  • Two scalar Numeric controls, and label them a (real scalar) and b (real scalar), respectively.
  • One scalar Numeric indicator, and label it z (real scalar).

  Enter values to these Front panel elements as on the Front panel of mathscript_example.

• Do the following with the Block diagram (re-position the elements as you wish):
  • Add a MathScript node from the Functions / Mathematics / Scripts & Formulas palette. In the node, type the commands as shown in the Block diagram of mathscript_example
  • Create input tunnels and output tunnels to the node by right-clicking on the border of the node, and give these inputs and outputs names as shown in the Block diagram of mathscript_example.
  • Connect the control terminals to the inputs of the MathScript node according to the Block diagram of mathscript_example. The data type of each input is then automatically set by LabVIEW, but you should check the settings by right-clicking on each of the inputs.
  • It turns out that the data type of the outputs are not set automatically by LabVIEW. In stead, you must set the data type manually by right-clicking on each of the outputs:
    • z: Scalar, DBL
    • y: Matrix, real

    Then connect the ouputs y and z to their respective indicators.

• Create an error indicator on the Front panel: Right-click on the error output (at the lower right corner of the MathScript node) / Create Indicator.

Save the VI, and run it. Does it work?

Note: This VI will run the code once since the code is not inside any While loop. If you want, you can add a While loop, a Stop button, and a Metronome. If you do not want to add a While loop, but still want to run your VI continuously while testing it, click the Run Continuously button in stead of the Run button in the toolbar.

Startup

Open the MathScript window (menu Tools / MathScript Window).

To get more space in the MathScript window, close the Workspace window (via the View menu in the MathScript window).

Execute the following commands in the Command window (by pressing the Enter button on the keyboard), and observe the results in the Output window. Below the commands are written in bold.

Entering commands

Here is a simple calculation:

1+2

The result is 3 (as you might have guessed) which is assigned to the standard variable ans (short for answer). ans always holds the result of the last command.

To add 4 to ans:

ans+4

ans now gets value 7.

Several commands may be written on one line, separating the commands using either semicolon or comma. With semicolon the result of the command is not displayed in the Output window, but the command is executed. With comma the result is displayed.

a=5; b=7, c=a+b

With the above commands the value of a is not displayed, while the values of b and c are displayed.

Recalling previous commands

To recall previous commands, press the Arrow Up button on the keyboard as many times as needed.

Arrow Up button

To recall a previous command starting with certain characters, type these characters followed by pressing the Arrow Down button on the keyboard. Try recalling the previous command(s) beginning with the a character:

a, then the Arrow Down button

Case sensitivity

MathScript is case sensitive:

C

MathScript says that C (capital) is an unknown symbol although the c (lowercase) variable exists.

Formating the output

Sometimes the output of a command is a large amount of numbers and/or text. It may be convenient, then, to show the results wrapped in the Output window.

As a start, make the following menu selection in the MathScript window: View / Output wrapped(so that the output is wrapped). Now, type the following command:

help format

Certainly the output is wrapped.

Now, make the menu selection so that the output is not wrapped (the same menu as above), and then repeat the command:

help format

The output is not wrapped.

I suggest you now select wrapping the output.

Help

Above you used the help command. It command displays information about a known command, typically including an example. Try

help sin

You can also search for information about a command via the Help / Search the LabVIEW Help menu in the MathScript window:

Search for information about the sin command in LabVIEW Help.

Number formats

The format command is used to select between different formats of the output, cf. the information about the format command that you saw above. Try the following commands:

format short, 100*pi (Comment: 5 digits, except possible trailing zeros, are shown.)

format long, 100*pi (16 digits.)

format short e, 100*pi (5 digits and a term showing the exponents of 10)

format long e, 100*pi (16 digits and a term showing the exponents of 10)

In most cases format short is ok. This is also the default format. To reset to format short:

format short

Entering numbers

You can enter numbers in various ways:

x1=0.1

x2=1e-1

x3=2e2

x4=2*10^(2)

x5=exp(1) (the natural base, e = e¹ = 2.7183)

x6=1+2i (a complex number)

The Workspace

All variables generated in a MathScript session (a session lasts between launching and quitting MathScript) are saved in the MathScript Workspace. You can see the contents of the Workspace using the menu Tools / Workspace / Variables (tab). Alternatively, you can use the who command:

who

You can delete a variable from the Workspace:

clear x6

who

The Workspace is cleared if you quit MathScript. You can however save variables in the Workspace into a file using the Save command, and restore the variables using the load command. (If you generate the variables by running commands in a MathScript script, it may be sufficient to just save the script, not the variables, and run the script when you need the variables.)

The MathScript Working Directory is the default folder when using the save or load commands. You can display, and change, the Working Directory via the File / MathScript Preferences / Working Directory menu, but you do not have to do this unless you are going to use the save or load commands.

As an alternative to displaying the Working Directory using the File / MathScript Preferences menu, you can also display the Working Directoy using the pwd command (Print Working Directory):

pwd

And you can change the Working Directory using the cd command.

MathScript functions are polymorphic, i.e. they typically take both scalars and vectors (arrays) as arguments. As an example, the following two commands calculate the square root of the scalar 2 and the square root of each of the elements of the vector of integers from 0 to 5, respectively:

sqrt(2)

sqrt([0,1,2,3,4,5])

When the argument is a vector as in this case, the calculation is said to be vectorized.

Matrices and vectors

The matrix is the basic data element in MathScript. A matrix having only one row or one line are frequently denoted vector. Below are examples of creating and manipulating matrices (and vectors).

To create a matrix, use comma to separate the elements of a row and semicolon to separate columns. For example, to create a matrix having numbers 1 and 2 in the first row and 3 and 4 in the second row:

A=[1,2;3,4]

with the result

A =

             1 2
             3 4
 

To transpose a matrix use the apostrophe:

B=A'

To create a row vector from say 0 to 4 with increment 1:

R1=[0:4]

To create a row vector from say 0 to 4 with increment 0.5:

R2=[0:0.5:4]

To create a column vector from say 0 to 4 with increment 1:

R3=[0:4]'

You can create matrices by combining vectors (or matrices):

C1=[1,2,3]'; C2=[4,5,6]'; M=[C1,C2]

Here are some special matrices:

zeros(2,3)

diag([1,2,3])

ones(3,2)

You can address an element in a matrix using the standard (row number, column number) indexing. Note: The element indexes starts with one, not zero. (In LabVIEW, array indexes starts with zero....) For example (assuming matrix A=[1,2;3,4] is still in the Workspace), to address the (2,1) element of A and assign the value of that element to the variable w:

w=A(2,1)

with result w=3.

You can address one whole row or column using the : (colon)operator. For example,

C2=A(2,:)

with result C2=[3,4] (displayed a little different in the Output window, though).

Element-by-element calculations

Element-by-element calculations are executed using the dot operator together with the mathematical operator. Here is an example of calculating the product of each of the elements in two vectors:

[1,2,3].*[4,5,6]

with result [4 10 18].

Scripts

Create a script in the Script editor (which is on the Script tab in the Workspace window (a new Script editor can opened via the menu File / New Script Editor) of name script1.m with the following contents:

a=1;
b=2;
c=a+b

Save the script in any folder you want.

Run the script by clicking the Run button. All the commands in the script are executed from top to bottom as if they were entered at the command line.

You should make it a habit to use scripts for all your work. In this way you save your work, and you can automate your tasks.

Plotting

You can plot data using the plot command (several addition plotting commands are available, too). Here is an example:

Generate a vector t of assumed time values from 0 to 100 with increment 0.1:

t=[0:.1:100]';

Generate a vector x as a function of t:

x=-1+0.02*t;

Generate a vector y as a function of t:

y=sin(0.2*t);

Open Figure no 1:

figure(1)

Plots x verus t, and y versus t, in the same graph:

plot(t,x,t,y)

The resulting plot is shown in the figure below.

The resulting plot

Probably you want to add labels, annotations, change line color etc. This can be done using menus in the Plot window. This is straightforward, so the options are not described here.

As an alternative to setting labels etc. via menus in the Plot window, these can be set using commands. Below is an example, which should be self-explaining, however note how the attributes to each curve in the plot is given, see the plot() line in the code below.

t=[0:.1:100]';
x=-1+0.02*t;
y=sin(0.2*t);
figure(1)
plot(t,x,'r--',t,y,'b-')  %x(t) in dashed red. y(t) in solid blue.
xmin=0;xmax=100;ymin=-2;ymax=2;
axis([xmin xmax ymin ymax])
grid
xlabel('t [sec]')
ylabel('x (red, dashed) og y (blue, solid) [Volt]')
title('Data from Experiment 1')

Plot generated by command-based configuration of the plot