creating a .mat file which is from a double in app designer

I am using app designer to create an application that takes two tabular columns from a .csv file that has 5 columns and can create it into a another .csv file with two columns and a .mat file with the same. I have managed to create the .csv file with the output but i cannot seem to find a way to create the .mat file. If anyone could help me out it would be highly appreciated. thanks

[dpb]

Show how you created the .csv file.

But, you go on to say you did create a .mat file and then that you couldn't...we can't debug what we can't see so show us.