The switch case names and the inputs for the switched variable response do not match here. The input response from the user is min or max or sum but the cases specified are min(x), max(x) and sum(x). Remove the (x) portion from the names and designate the case names as strings. Also, the input to the lower function here should be the variable response not the string 'response'. The cleaned up code should look like this:
t = [0:100];
x = exp(-t).*sin(t);
response = input ('Type min, max, or sum. ','s')
response = lower(response);
switch response
case 'min'
minimum = min(x)
case 'max'
maximum = max(x)
case 'sum'
total = sum(x)
otherwise
disp('You have not entered a proper choice.')
end
