How to Have a User Input a Matlab Function?

Hello! I need to writea script that has a user enter the name of any trigonemtric function that will be used to find the sin,cos,tan,etc of an array. How would I go about doing this? Right now I just have:

n=input('Please input a positive number n: ');
b=input('please enter a trigonemtric function name (cos,sin,tan,etc.): ','s');
x=linspace(0,n,1000)

Thank you and any help is much appreciated!