查看“特殊值 !Values”的源代码

: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

:F_INFINITY可以和浮点数做比较 F_NAN不能
 B = [1.0, 2.0, !VALUES.F_NAN]
 IDL> PRINT, WHERE(B EQ !VALUES.F_NAN
          -1
:在求平均等计算时，设置/NAN开关，可将这些数忽略
 IDL> print,mean(B)
          NaN
 IDL> print,mean(B,/NAN)
      1.50000