Sometimes, if you set a breakpoint in a function, and then attempt to view the value of a variable in the parent workspace using the dbup command, the value of the variable is currently under construction. Therefore, the value is not available. This is true whether you view the value by specifying the dbup command in the Command Window or by using the Stack field on the Editor toolbar.
In such cases, MATLAB returns the following message, where x is the variable for which you are trying to examine the value:
K>> x
??? Reference to a called function result under construction x.
For example, suppose you have code such as the following:
x = collatz(x);
MATLAB detects that the evaluation of collatz(x) replaces the input variable, x. To optimize memory use, MATLAB overwrites the memory that x currently occupies to hold a new value for x. When you request the value of x, and it is under construction, its value is not available, and MATLAB displays the error message.
