Char vs String detection

[YuchenWu2001]

When running lecture13.m, the following error was reported:

>> lecture13
Dot indexing is not supported for variables of this type.

Error in step (line 15)
            xnew = x + dynamics.f(x,u).*dt;

Error in roll_out (line 45)
            xlist(:,k+1) = step(xlist(:,k), ulist(:,k), dt, dynamics, simmode);

Error in lecture13 (line 27)
[tlist, x_fb, u_fb] = roll_out(sys.name, ufb, sys.x0, 'DT', simhorizon, sys.dt, 'Euler');

The reason seems to be the dynamics variable (with content ‘double_intergrator') was detected as a char instead of a string

K>> isa(dynamics, 'string')

ans =

  logical

   0

K>> isa(dynamics, 'char')

ans =

  logical

   1

My temp fix to the problem: replace line 13 of step.m to be:

if isa(dynamics, 'string') | isa(dynamics, 'char')