Programming and Data Types

Persistent Variables

Characteristics of persistent variables are

• You can only use them in functions.
• Other functions are not allowed access to them.
• MATLAB does not clear them from memory when the function exits, so their value is retained from one function call to the next.
• If you clear the function or edit the M-file for that function, then MATLAB clears all persistent variables used in that function.

You must declare persistent variables as persistent before you can use them in a function. It is usually best to put persistent declarations toward the beginning of the function. You wouldl declare persistent variable SUM_X as follows:

• persistent SUM_X
  

You can use the mlock function to keep an M-file from being cleared from memory, thus keeping persistent variables in the M-file from being cleared as well.

Global Variables

Special Values