IF  IF-ELSEIF-ELSE Conditional Statements


Usage
 
 The if and else statements form a control structure for
 conditional execution.  The general syntax involves an if
 test, followed by zero or more elseif clauses, and finally
 an optional else clause:
 
   if conditional_expression_1
     statements_1
   elseif conditional_expression_2
     statements_2
   elseif conditional_expresiion_3
     statements_3
   ...
   else
     statements_N
   end
 
 Note that a conditional expression is considered true if 
 the real part of the result of the expression contains
 any non-zero elements (this strange convention is adopted
 for compatibility with MATLAB).
 