PART 1: scalars and arrays

Contents

scalars

MATLAB variables can represent scalar (single-element) quantities.

a = 2;
b = 3;
c = a + b

c =

     5

arrays (vectors)

MATLAB variables can also represent arrays or matrices

a = [1 2 3 4];
b = [4 5 6 7];
c = a + b

c =

     5     7     9    11

Even though you may not make the distinction, MATLAB always treats arrays
as vectors.  MATLAB has two ways of representing vectors: row vectors
and column vectors

this is a row vector

a = [1 2 3 4]

a =

     1     2     3     4

and this is a column vector

b = [4; 5; 6; 7]

b =

     4
     5
     6
     7

You cannot add a row vector to a column vector. Trying to do so results in a error message. (we'll discuss the "try" and "catch" commands later... they are used here to allow execution to continue after the error)

try
    c = a + b
catch
    lasterr
end

ans =

Error using ==> plus
Matrix dimensions must agree.

finding array sizes

there are several ways to check on the size of an array to find out if it is a row- or column-vector, including the size command and the whos command.

size

The size command returns the size of a scalar, vector or matrix. The answer is a row vector with the number of rows and columns.

size(a)

ans =

     1     4

size(b)

ans =

     4     1

as you can see, a is a row vector (1 row, 4 columns) and b is a column vector (4 rows, 1 column).

whos

The whos command lists all the variables in the current workspace, together with information about their size, bytes, class, etc.

whos

  Name       Size                    Bytes  Class

  a          1x4                        32  double array
  ans        1x2                        16  double array
  b          4x1                        32  double array
  ball       1x1                       560  struct array
  c          1x4                        32  double array

Grand total is 26 elements using 672 bytes

whos var1 var2... restricts the display to the variables specified.

whos a b

  Name      Size                    Bytes  Class

  a         1x4                        32  double array
  b         4x1                        32  double array

Grand total is 8 elements using 64 bytes

as we can see from above, a and b have different sizes therefore we cannot add them together directly.

adding row and column vectors of the same length

Sometimes in MATLAB, you'll end up with one variable that's a row vector and one that's a column vector. Here are some ways to add them together, provided they have the same length (number of elements.

transpose a

c = a' + b

c =

     5
     7
     9
    11

transpose b

c = a + b'

c =

     5     7     9    11

force a and b to both be column vectors (this works under the broadest range of conditions)

c = a(:) + b(:)

c =

     5
     7
     9
    11

subscripts, referencing individual array elements

the third element of a

a(3)

ans =

     3

first three elements of b

b(1:3)

ans =

     4
     5
     6

the last element of a

a(end)

ans =

     4

Published with MATLAB® 7.0