查看“IDL中的系统变量”的源代码

* !Values
:NAN and Infinity value 

 IDL> help,!Values,/str
 ** Structure !VALUES, 4 tags, length=24, data length=24:
   F_INFINITY      FLOAT               Inf
   F_NAN           FLOAT               NaN
   D_INFINITY      DOUBLE            Infinity
   D_NAN           DOUBLE                 NaN
 Inf还可取负
 IDL> print,-1*!Values.F_INFINITY
         -Inf
 问题：如何给一个整数变量赋一个NAN 或者 INFINITY

*!EXCEPT
:数学错误
   !EXCEPT=0 不报错.
   !EXCEPT=1 （默认值，在程序结束后回到交互控制台报错）
   !EXCEPT=2 （在出错的地方报错）
在涉及到NaN的数据运算时，容易出现数学错误，比如
    A = [1.0, 2.0, !VALUES.F_NAN]
    PRINT, WHERE(A GT 1.0)
    IDL prints:
      1
    % Program caused arithmetic error: Floating illegal operand
:该问题可利用FINITE函数加以解决。如
 PRINT, WHERE(FINITE(A) EQ 1)
在程序中如果设置！EXCEPT＝0，可以用CHECK_MATH加以监控
:result＝ check_math，check_math的数值如下

      0     
      No errors detected since the last interactive prompt or call to CHECK_MATH
      1     
      Integer divided by zero
      2     
      Integer overflow
      16     
      Floating-point divided by zero
      32     
      Floating-point underflow
      64     
      Floating-point overflow
      128     
      Floating-point operand error. An illegal operand was encountered, such as a negative operand to the SQRT or ALOG functions, or an attempt to convert to integer a number whose absolute value is greater than 231 - 1