function y = calculate(func, x)
%
% given the name of some mathematical function, and a value 'x',
%   call the mathematical function with 'x' as an argument.
%   Return the resulting value.
%   
%   Arguments:
%   
%           func              (input)   a string, the name of a mathematical 
%                                            function which we will call
%                                             
%           x                 (input)   value at which to evaluate the
%                                            function

  y = feval(func, x);

%  end of calculate function
