This was my attempt at an interactive linear algebra program. What resulted was basically an extremely small subset of MATLAB.
The program can do some basic matrix operations (multiplication, addition and subtraction) and can even do those operations on single numbers (although they are stored internally as 1x1 matrices). The main purpose of the program was originally to test two common linear algebra algorithms. LU decompostion and QR (and it's more numerically stable cousin Modified Grahm Schmidt) decompostion.
From a programming side this is somewhat interesting in that I implemented variables so you can do things like A = 1 and then A * 2, etc. I also implemented something that is more or less a parse tree so it can handle arbitrary legal expressions up to a certain length. Less interesting is that the syntax relies on spaces between every token. Also rather annoying is that odd matrix syntax I devised (probably on the fly) as I was writing this. The begginning and end of a matrix isn't specified (although it may be wrapped in paranthesis) and pipes ("|") are used to delimit rows.
An example would be A = 1 1 | 1 1
This produces a 2x2 matrix of all ones.
Lastly, in order to test the output of the algorithms I implemented reading matrices from files and writing matrices to files in a simple format that MATLAB supports.
Write takes a file name and writes a variable currently in memory into it.
write file_name var
Read takes a file name and read its contents into a variable which may be new.
read file_name var
Below is a link to the source code. Feel free to take a look or compile and try it out, a makefile is included. This code is released under the BSD license.linear_algebra_jp.tar.bz2