Page 370 - Process Modelling and Simulation With Finite Element Methods

A MATLAB/FEMLAB Primer for Vector Calculus 351

>>a= [1234; 56781;
>> size(a)
ans =
2 4
Size of an array is itself a row vector of length equal to the array dimensions.
>> length (a (1, ) )
:
ans =
4
The colon (:) placeholder in the second argument of a specifies the entire range
of the second dimension, in this case elements 1 :4, i.e. 1 thru 4.
>> length(a(:,3))
ans =
2
>> a(1,2:4)
ans =
2 3 4
In fact, the colon refers to subarrays of a lower dimension. a( 1,:) is the first row;
a(:,3) is the third column of a. a(1, 2:4) gives a subarray of elements 2 thru 4 of
row 1. In higher dimensions, the subarrays extracted are more complicated. For
instance

>> b(1, :)
ans =
1 1 1 1
Here, the subarrays are matrices in the first two cases, but in the third case, the
final two dimensions are rolled up into a single row vector.

FORTRAN programmers will probably feel more comfortable addressing single
elements

rather than subarrays, perhaps by using looping structures.

Array Construction
Arrays can be automatically generated using colon notation, viz.