2.1 Lab 2: labview mathscript and hybrid programming  (Page 2/6)

>>x=[1,2,3,4,5,6]

Alternatively, use the notation ‘:’

>>x=1:6

This notation creates a vector starting from 1 to 6, in steps of 1. If a vector from 1 to 6 in steps of 2 is desired, then type:

>>x=1:2:6

ans =

1 3 5

Also, examine the following code:

>>ii=2:4:17

>>jj=20:-2:0

>>ii=2:(1/10):4

One can easily extract numbers in a vector. To concatenate an array, the example below shows how to use the operator ‘[ ]’:

>>x=[1:3 4 6 100:110]

To access a subset of this array, try the following:

>>x(3:7)

>>length(x) % gives the size of the array or vector

>>x(2:2:length(x))

Allocating memory

One can allocate memory for one-dimensional arrays (vectors) using the command zeros. The following command allocates memory for a 100-dimensional array:

>>y=zeros(100,1);

>>y(30)

ans =

0

One can allocate memory for two-dimensional arrays (matrices) in a similar fashion. The command

>>y=zeros(4,5)

defines a 4 by 5 matrix. Similar to the command zeros, the command ones can be used to define a vector containing all ones,

>>y=ones(1,5)

ans=

1 1 1 1 1

Special characters and functions

Some common special characters used in .m files are listed below for later reference:

Some special functions are listed below for later reference:

Here is an example of the function length ,

>>x=1:10;

>>length(x)

ans =

10

The function find returns the indices of a vector that are non-zero. For example,

I = find(x>4) finds all the indices of x greater than 4. Thus, for the above example:

>>find(x>4)

ans =

5 6 7 8 9 10

Control flow

.m files have the following control flow constructs:

• if statements

• switch statements

• for loops

• while loops

• break statements

The constructs if, for, switch and while need to terminate with an end statement. Examples are provided below:

if

>>x=-3;

if x>0

str='positive'

elseif x<0

str='negative'

elseif x== 0

str='zero'

else

str='error'

end

See the value of 'str' after executing the above code.

while

>>x=-10;

while x<0

x=x+1;

end

See the value of x after executing the above code.

for loop

>>x=0;

for j=1:10

x=x+j;

end

The above code computes the sum of all the numbers from 1 to 10.

break

With the break statement, one can exit early from a for or a while loop:

>>x=-10;

while x<0

x=x+2;

if x = = -2