Hello Huang, Could you provide a small, self contained example which illustrates the error you are getting? Without seeing your code, I'm not quite sure what to say. -Zach (VIS)

Thanks Zach, An example is something like this: IDL> a = [[findgen(10)],[findgen(10)]] IDL> help, a A FLOAT = Array[10, 2] IDL> b = [[[a]],[[a]]] IDL> help, b B FLOAT = Array[10, 2, 2] IDL> c = [[[[b]]],[[[b]]]] c = [[[[b]]],[[[b]]]] ^ % Only three levels of variable concatenation are allowed. I am expecting to have an array C like this: Help, C C FLOAT = ARRAY[10, 2, 2, 2]