Chapter 5
package related, reading/writing Mathematica source code to/from files, contexts and related

5.1 How to write a package?

Small note here

5.2 How to use context and packages?

?$Packages

"gives a list of the contexts corresponding to all packages which have been loaded in your current Mathematica session."

{"JLink`", "GetFEKernelInit`", "ResourceLocator`", 
"PacletManager`", "QuantityUnits`", "WebServices`", 
 "System`", "Global`"}
 

5.3 How to find what packages are loaded?

$ContextPath

{"PacletManager`", "QuantityUnits`", "WebServices`", 
"System`", "Global`"}
 

5.4 Finding packages in specific context

Names["System`ComplexExpand`*"]

 
{"System`ComplexExpand`AbsExpr", 
"System`ComplexExpand`ArgExpr", 
"System`ComplexExpand`ConjugateExpr", 
"System`ComplexExpand`ReImExpr", 
"System`ComplexExpand`ReImFail", 
"System`ComplexExpand`SignExpr"}
 

5.5 How to find what contexts are loaded?

?Contexts

Contexts[] gives a list of all contexts. 
Contexts["string"] gives a list of the contexts 
                   which match the string.
 

5.6 How to load an m file or a package?

Append to the Path the folder name where the package is located in. In this example, assuming there is a package control.m located in folder C:\data then type the following to load the package

AppendTo[$Path, "C:\\data"] 
<< control.m
 

5.7 Finding names of functions in a package

$Packages	{"JLink`", "GetFEKernelInit`", "ResourceLocator`", "PacletManager`", "QuantityUnits`", "WebServices`", "System`", "Global`"}
Names["JLink`*"]	{"JLink`AddPeriodical", "JLink`AddToClassPath",...

5.8 Finding a package that has specific function

use Context.

Context[Integrate] 
 
     "System`"
 

5.9 Finding all contexts that belong to a package?

Contexts["packageName*"]
 

5.10 How to remove packages?

to do

5.11 How to list files in a directory?

SetDirectory[$BaseDirectory]; 
FileNames["*"]
 

5.12 Where is init.m and how to use it?

Possible locations for init.m files include the following:

1. $BaseDirectory/Kernel kernel initialization code for all users
2. $UserBaseDirectory/Kernel kernel initialization code for the currently logged-in user
3. $BaseDirectory/FrontEnd front end initialization code for all users
4. $UserBaseDirectory/FrontEnd front end initialization code for the currently logged-in user

5. I have my init.m in the following folder

   C:\Documents and Settings\All Users\Application Data\Mathematica\Kernel\init.m

5.13 Reading Mathematica example data and location

on windows, V 8, example data is located in

C:\Program Files\Wolfram Research\Mathematica\8.0\Documentation\English\System\ExampleData
 

and it can be read like this

str = OpenRead["ExampleData/USConstitution.txt"] 
 
Out[147]= InputStream[ExampleData/USConstitution.txt, 127]
 

5.14 Finding which folders are on trusted path

Thanks to Mike for these commands, see http://stackoverflow.com/questions/8583521/wh y-do-i-get-security-warning-message-this-file-contains-potentially-unsafe-dyn

CurrentValue[$FrontEnd, {"NotebookSecurityOptions", "TrustedPath"}] 
 
Out[212]= {FrontEnd`FileName[{$InstallationDirectory}], 
          FrontEnd`FileName[{$BaseDirectory}], 
          FrontEnd`FileName[{$UserBaseDirectory}]} 
 
CurrentValue[$FrontEnd, {"NotebookSecurityOptions", "UntrustedPath"}] 
 
Out[213]= {FrontEnd`FileName[{FrontEnd`$DesktopDirectory}], 
           FrontEnd`FileName[{FrontEnd`$DownloadsDirectory}], 
  FrontEnd`FileName[{FrontEnd`$LocalApplicationDataDirectory}], 
  FrontEnd`FileName[{FrontEnd`$RemoteApplicationDataDirectory}], 
  FrontEnd`FileName[{FrontEnd`$ProgramFilesDirectory}], 
  FrontEnd`FileName[{FrontEnd`$ProgramFilesX86Directory}], 
  FrontEnd`FileName[{$TemporaryPrefix}]}
 

Now to find if your current notebook is on the trusted path type NotebookDirectory[] and see if the output shows up in the trusted path of not. To add a folder to trusted path go to "Preferences > Advanced > Open Options Inspector". Then under Global Preferences search for trusted

5.15 save matrix to file, and read it again

SetDirectory[NotebookDirectory[]]; 
list = {{3, 4, 5}, {4, 5, 6}}; 
Export["data.txt", list]
 

To read it later, say after closing and restarting Mathematica again to continue working on the data

SetDirectory[NotebookDirectory[]]; 
list = ToExpression@Import["data.txt", "List"] 
 
    {{3, 4, 5}, {4, 5, 6}}
 

5.16 run Mathematica m file as script

Thanks to Rolf Mertig reference for help on this.

Make a file foo.m such as

AppendTo[$Echo, "stdout"] 
SetOptions[ $Output, FormatType -> OutputForm ]; 
Integrate[Sin[x],x]
 

Now type, from DOS window

"C:\Program Files\Wolfram Research\Mathematica\10.1\math.exe" < foo.m
                                                                                    
                                                                                    
 

This will send input and output to screen. To send output to file do

"C:\Program Files\Wolfram Research\Mathematica\10.1\math.exe" < foo.m > log.txt
 

You can modify the PATH on windows to add the above to environment variable so not to have to type the long command each time