Page 24 - MATLAB Recipes for Earth Sciences

2.3 The Syntax 15

2.3 The Syntax

The name MATLAB stands for matrix laboratory. The classic object handled
by MATLAB is a matrix, i.e., a rectangular two-dimensional array of num-
bers. A simple 1-by-1 matrix is a scalar. Matrices with one column or row
are vectors, time series and other one-dimensional data fi elds. An m-by-n
matrix can be used for a digital elevation model or a grayscale image. RGB
color images are usually stored as three-dimensional arrays, i.e., the colors
red, green and blue are represented by a m-by-n-by-3 array.
Entering matrices in MATLAB is easy. To enter an arbitrary matrix, type
A = [2 4 3 7; 9 3 -1 2; 1 9 3 7; 6 6 3 -2]

after the prompt, which fi rst defines a variable A, then lists the elements of

the matrix in square brackets. The rows of A are separated by semicolons,
whereas the elements of a row are separated by blanks, or, alternatively, by
commas. After pressing return, MATLAB displays the matrix
A =
2 4 3 7
9 3 -1 2
1 9 3 7
6 6 3 -2

Displaying the elements of A could be problematic in case of very large ma-
trices, such as digital elevation models consisting of thousands or millions
of elements. In order to suppress the display of a matrix or the result of an
operation in general, you should end the line with a semicolon.

A = [2 4 3 7; 9 3 -1 2; 1 9 3 7; 6 6 3 -2];
The matrix A is now stored in the workspace and we can do some basic op-
erations with it, such as computing the sum of elements,
sum(A)

which results in the display of

ans =
18 22 8 14

Since we did not specify an output variable, such as A for the matrix entered
above, MATLAB uses a default variable ans, short for answer, to store the
results of the calculation. In general, we should define variables since the

next computation without a new variable name overwrites the contents of
ans.