Why am I getting this error, "Subscript indices must either be real positive integers or logicals."

% This code worked the last time I ran it but now I get an error message. Why is this?

      t = [-2: .001: 1.999];
      mt = sinc(5 .* t ./ pi);

      figure(1);
      plot(t, mt);
      xlabel('time');
      ylabel('amplitude');
      title('m(t)=sinc(5t/pi)');
      grid;

      PM = cos(50 .* pi + 20 .* mt);

      figure(2);
      plot(t, PM);
      xlabel('time');
      ylabel('amplitude');
      title('PM Signal');
      grid;

      % cumsum function is used to calculate integral
      integral_mt = cumsum(mt) .* 0.001;
      FM = cos(50 .* pi + 40 .* pi .* integral_mt);

      figure(3);
      plot(t, FM);
      xlabel('time');
      ylabel('amplitude');
      title('FM Signal');
      grid;

Answer 1

[Walter Roberson]

Works for me. You probably defined a variable named sinc or plot or cos

Answer 2

[Porgs]

Thank you that was the problem.