"...change the data types of a signal directly in .mat file"
Can you more fully explain what you're needing and attach a (smallish) example .mat file?
If you mean to change (for example) a double to a single in a .mat file, that is only possible by reading the variable from the .mat file, converting it to whatever other datatype is desired and then re-saving it.
save will overwirte an existing variable in a .mat file with the new content, effectively changing its type, but it can't be done with a typecast() while the variable is in the file, only on a copy in memory.
Does
x=rand(10,1);
y=sqrt(x);
whos
save test
whos -file test
y=single(y);
save test y -append % must append or will wipe out x leaving only y
whos -file test
do the kind of thing you're looking for?
