But, presuming 'ps' means to do both 'p' and 's', you need that case as well as written anyway because in Matlab the switch block case statements do NOT "fall through" as in C.
opt=input('Which velocity model(s)? Enter p, s, or ps: ','s'); % return string
if contains(opt,'p')
% code to extract P velocity from P velocity text file
end
if contains(opt,'s')
% code to extract S velocity from S velocity text file
end
does either or both and is also insensitive to your user entering 'sp' instead of 'ps'. Of course, it will also do both if user enters 'stop' so should probably do some input verification as well.
