Memory Management Tools

While Mathematica is designed to manage memory for you, under certain circumstances it can get bogged down, mainly because it keeps a record of all your inputs and outputs with In and Out. So if you're using functions that output a lot of computation, or working with large files, you may notice Mathematica slowing down.

There are a number of ways that you can manage memory in Mathematica. Here is a summary (see also How to Find Memory Used in Computations).

Command	Effect
?Global`*	Shows all Symbols in a non-accessible table
Names@”Global`*”	Returns a List of all Symbols that you can access
Clear@symbol	Clears the value of symbol but leaves its name in memory
Clear@”Global`*”	Clears the values of all Symbols but leaves their names in memory
Remove@symbol	Removes the name symbol and its value from memory
Remove@”Global`*”	Removes all Symbols and their values from memory

If you're going to go as far as removing all Global Symbols, consider starting a new session by entering Quit[] in your Notebook or Quit Kernel → Local under the Evaluation menu.

Beginners hesitate to Quit the kernel, but there's little downside. Even if you haven't saved your Notebooks, the kernel is a separate entity and you can save them.

To automate resuming after quitting the kernel or in general, use Initialization Cells. You can set Initialization in the menu under Cell → Cell Properties or by right-clicking on the cell and selecting Initialization Cell. A little downward tick mark appears in the upper right corner of the cell.

Then when you re-start the kernel by selecting any cell, selecting Evaluation → Evaluate Initialization Cells, or re-open the Notebook, all the Initialization cells are automatically re-Evaluated. In this way you lose very little time by quitting the kernel and re-starting.

Memory-Management Commands to Use Occasionally

Memory currently used by the kernel:

In[157]:= MemoryInUse[]

Out[157]= 135450976

Memory currently used by the front end (all of your open Notebooks):

In[158]:= MemoryInUse@$FrontEnd

Out[158]= 543264768

The maximum memory used by the kernel during your current Mathematica session:

In[159]:= MaxMemoryUsed[]

Out[159]= 137155304

Clear a cell that consumed lots of memory in your session:

Unprotect[Out]; Out[537] =.;
Protect@Out;