TF = ISVALID(H) performs an element-wise check for validity on the 
handle elements of H.  The result is a logical array of the same 
dimensions as H, where each element is the element-wise validity 
A handle is invalid if it has been deleted or if it is an element
of a handle array and has not yet been initialized.
See also SWPREF, SWPREF/DELETE Help for swpref/isvalid is inherited from superclass HANDLE
Reference page in Doc Center
   doc swpref/isvalid