why often it takes a very very long time to show the results by using findsym?

Hi everyone, these days I am using symbolic computation in Matlab.

to substitute the symbol with numerical results, i need to find which symbols in a variable. So the code findsym is applied. However, it takes often quite a long long long time to show the symbols of a variable, as if the results cannot be exhibited in the command window. But it sometimes can show the results of some other counterparts in a reasonable time. However, these variables have the similar complexity, and according to theoretical deduce, they should have the same set of symbols in them. In my file, there are ten symbolic variables in sum. Could anyone tell me what i should do to get the results of findsym ? Thanks very much!