MATLAB Tips and Previews

• The latest release of MATLAB (MATLAB 5.2) added the "persistent" declaration to the language. Persistent variables have function scope and retain their value between function calls.

• P-files created in MATLAB 5.2 or 5.1 will not execute in MATLAB 5.0. The reverse is true, however: P-files created with MATLAB 5.0 will execute in MATLAB 5.0, 5.1 and 5.2.

• Contrary to what it says on page 54 of Mastering MATLAB 5,

  d+zeros(n,m)

  is the fastest way to generate an array containing the scalar value d in all its locations.

  repmat(d,n,m) is typically the slowest method, which is contrary to the help text for repmat! The only time repmat is fast is when the final array is nearly square.

• Version 5.2 of MATLAB introduces two new user-interface features:

  Contextual Menus, i.e., menus that pop up under the mouse. These are a new object type uicontextmenu to go along with uicontrol and uimenu object types. Uicontextmenus are essentially uimenu objects associated with handle graphics objects such as lines, axes, etc.

  There is a new uicontrol style called a togglebutton. This appears as a pushbutton uicontrol which toggles on and off like a radio button. Toggle Button uicontrols can be used to implement toolbars such as those that appear in MS products, the MATLAB Command Window and Editor Window. The btngroup function uses toggle buttons to implement toolbars.

• The fopen function takes a third argument to specify the byte order of a data file. Mastering MATLAB 5 (on page 35) fails to mention this third argument. MATLAB calls this the MACHINEFORMAT argument. Subsequent fread or fwrite calls will read or write the data in the specified format as shown below:

  'native'	or	'n'	local machine format - the default
  'ieee-le'	or	'l'	IEEE floating point with little-endian byte ordering
  'ieee-be'	or	'b'	IEEE floating point with big-endian byte ordering
  'vaxd'	or	'd'	VAX D floating point and VAX ordering
  'vaxg'	or	'g'	VAX G floating point and VAX ordering
  'cray'	or	'c'	Cray floating point with big-endian byte ordering
  'ieee-le.l64'	or	'a'	IEEE floating point with little-endian byte ordering and 64 bit long data type
  'ieee-be.l64'	or	's'	IEEE floating point with big-endian byte ordering and 64 bit long data type.

  In addition, the form [filename,permission,machineformat]=fopen(fid) returns the filename, permission, and machineformat associated with the given file identifier. You can determine your native byte order by issuing the command [fn,pm,mf]=fopen(1);

• The cd and pwd commands return the path to the current directory. Under MATLAB 5.2 on the Macintosh platform this string includes a trailing pathsep character (a colon on the Mac). This has changed from earlier versions (such as 5.0 for the Mac). It seems to occur only in version 5.2 and only on the Macintosh platform. This bug (feature?) could break your M-files.

• The next release of Matlab (v5.3?) will have support for a uint16 datatype in addition to the current uint8 datatype for images.

The Mastering MATLAB Toolbox

Questions and comments regarding Mastering MATLAB, Mastering MATLAB 5, and the Mastering MATLAB Toolbox can be sent via e-mail to: mm@eece.maine.edu. We welcome all comments, bug reports, errata, and suggestions for future editions.