Matlab too many input arguments using csvread
You should improve your question and it seems not being related with arduino at all. However, what I think you are trying to do is to auto generate the name of the file you use in cvsread accordingly to the value of y. This can be done using sprintf, in your case for the first expression csvread(sprintf('t%d_25.csv',y),1,1).
Although, the structure of your code seems really messy take a look at your end instructions.