how to create .mat file from .csv file??

I have a .csv datset which has 3 columns. I want to create .mat file from it.I tried many codes like:

M=importdata('dataset')
save('dataset.mat','M') 
and

M=importdata('dataset')
system('rename dataset dataset.mat');
It creates the .mat file,
but I dont know how to define the variables?
Kindly help