Read and write matrices as ASCII text files.
The file format is like:
MATRIX -- header 100 100 -- width and height 1.23 1.56 1.23 ... -- data, separated by whitespace ....
Read a matrix from a text file.
WARNING: This is implemented fairly naively, just using
under the covers. It will be slow for large data files.
It also doesn't do graceful error handling.
If the file has the wrong format you'll get a confusing