变量转换

浮点数转成整数

• round:四舍五入

IDL>print,round(5.1),round(5.9)
IDL> 5, 6

• ceil:向上进

IDL>print,round(5.1),round(5.9)
IDL> 6, 6

• floor:截取整数

IDL>print,round(5.1),round(5.9)
IDL> 5, 5

• 整数范围很小（long），要转换大的整数，加上/L64
• astro_lib中的nint程序，可以代替round，而且

(1) if no absolute value exceeds 32767, then the array is returned as a type INTEGER instead of LONG

(2) NINT will work on strings, e.g. print,nint(['3.4','-0.9']) will give [3,-1], whereas ROUND() gives an error message