< M A T L A B (R) > Copyright 1984-2018 The MathWorks, Inc. R2018a (9.4.0.813654) 64-bit (glnxa64) February 23, 2018 To get started, type one of these: helpwin, helpdesk, or demo. For product information, visit www.mathworks.com. >> sigma -1 ans = 'command' >> eval ('sigma -1') ans = 'command' >> sigma = 1 sigma = 1 >> sigma -1 ans = 'command' >> eval ('sigma -1') ans = 'command' >> foo () Error: File: /***/test-files/foo.m Line: 2 Column: 3 "sigma" was previously used as a variable, conflicting with its use here as the name of a function or command. See "How MATLAB Recognizes Command Syntax" in the MATLAB documentation for details. >> foo (1) Error: File: /***/test-files/foo.m Line: 2 Column: 3 "sigma" was previously used as a variable, conflicting with its use here as the name of a function or command. See "How MATLAB Recognizes Command Syntax" in the MATLAB documentation for details.