Why does the "matfile" function create files larger in size compared to the "save" function?

Comparing "matfile" and "save" with "-v7.3" shows different file sizes if the variables are objects (e.g. tabular classes, or Simulink objects like "Simulink.Signal").

If you save certain variables (object, e.g., tabular classes, or Simulink objects like "Simulink.Signal") with "save" (option "-v7.3"), the resulting file size is much smaller compared to using the "matfile" function to update existing variables in the MAT file.

Answer 1

[MathWorks Support Team]

This is a known limitation when updating existing variables in a MAT-File: the MAT-File's size can increase, especially if the variable is an object. Using the "matfile" object to update variables is equivalent to using "save" with the "-append" flag. Therefore, you see the size increase using the "matfile" object and using "save" with "-append". 

The only workaround is to re-save to a new MAT-File, using "save" or "matfile" object (to a new MAT-File). This would create a whole new file, and the size would be, as one would expect.

This is also documented in this Bug Report.