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;

Mathematica Keyboard Shortcuts

Keyboard Shortcuts and Handy Short Commands

Here are some useful and lesser-known keyboard shortcuts. In terms of saving time, rather than using brackets for single-argument functions, use Prefix: function@argument.

Likewise, nesting functions with increasingly distal matched brackets is difficult to read, increases programming time, and obstructs you highlighting what you feel is important in the function. Use Postfix-style with pure Functions like this:

dataFiles[[1]]//Rest//Flatten//Length;

dataFilesDifferences//Chop[#,10^-4]&//Union/@#&//ListPlot/@#&//Partition[#,3]&//Grid

As advocated in my 2007 User Conference talk (also here), a "Functional-Procedural Fusion" elegantly represents deeply nested functions in a readable manner. If you do use deeply nested functions, multiple-clicking the Head of an Expression will select its brackets.

Ctrl+F6          Switch between open Mathematica notebooks
F12                Toggle current notebook to and from full screen

Ctrl+Shift+K  After a function name gives you a template for the simplest form of the function

Ctrl+K            After a function name gives a drop-down listbox with autocompletions of the function

?*name*         As in "?*Plot*" lists all Mathematica functions with Plot in their name. You can then click on them to get quick help text.

?Global`*       Lists all Names created in current Mathematica session

F1                  Search Help for expression to left of cursor

Shift + F1      Open new instance of Help browser. Do scratchpad calcs in Help rather than opening a new Notebook. They're automatically cleaned up when you go to a new Help topic.

Alt+.              Interrupt a computation. If it doesn't work, do Evaluation/Quit Kernel.
Shift+Alt+.    Remove a selected computation from the Evaluation queue. This is handy when you have a long computation running, start another one, and want to abort that one without aborting the one that is running.

Rather than using palettes, just learn keyboard shortcuts for the symbols you use frequently, for example:

esc+[character}+esc  E.g. to give the Greek letter corresponding to the keyboard character
Ctrl+6             Superscript
Ctrl+-              Subscript
Alt+7              Format cell as plain text
Alt+6              Format cell as Subsubsection
Alt+5              Format cell as Subsection

%+Out line    As: %127. Refers to output line #127. Same as Out@127 or Out[127] but more concise. I use this frequently for a temporary variable name but if it turns out I need a more permanent mnemonic name I just create one: newName = %127. I use %, %%, or %2 only for very temporary "scratchpad" calcs.

Ctrl+L            Copy input cell from the one just above
Ctrl+Shift+L   Copy output cell from the one just above, into new input cell. An alternative is to just start typing in the Output cell and Mathematica automatically creates a new Input cell with those contents.

Clear@%127  Removes from memory some huge expression you created or imported in In[127].
ClearAll["Global`*"] and Remove["Global`*"] Clears or Removes all values from variables you created in the current session. If it comes to that, I usually kill the kernel though (Evaluation/Quit Kernel).

filePath="C:\\directory1\\directory2"; FileNameSetter@Dynamic@filePath

Gives you a in-Notebook button to click to navigate and select a filename or directory to which to Set filePath. Giving filePath an initial value before evaluating FileNameSetter takes you to that value (e.g. a directory) when you click the button. Using Dynamic lets you click the button over and over to re-Set filePath.

CreateDocument@expression Opens a new Mathematica notebook with expression in it. Expression can be an imported document.