>> pkg load symbolic
>> syms y(t)t
Symbolic pkg v2.8.0: Python communication link active, SymPy v1.4.
error: invalid symfun expression
error: called from
    assert at line 94 column 11
    syms at line 167 column 7
>> egy= diff(y(t),t)==-y/20
error: 't' undefined near line 1 column 13
>>
>> syms y(t)t
error: invalid symfun expression
error: called from
    assert at line 94 column 11
    syms at line 167 column 7
>> syms y(t) t
>> egy= diff(y(t),t)==-y/20
egy = (sym)

  d          -y(t)
  --(y(t)) = ------
  dt           20

>> dsolve(egy)
ans = (sym)

             -t
             ---
              20
  y(t) = C1*e

>> matlabFunction(rhs(dsolve(egy)))
ans =

@(C1, t) C1 .* exp (-t / 20)

>> dsolve(egy, y(0)==10)
ans = (sym)

             -t
             ---
              20
  y(t) = 10*e

>> f = @(t,y) -y/20 ;
>> tb = -4:4
tb =

  -4  -3  -2  -1   0   1   2   3   4

>> yb = 0:10;
>> [T,Y] = meshgrid([-2,2][3,4,5,6])
parse error:

  syntax error

>>> [T,Y] = meshgrid([-2,2][3,4,5,6])
                           ^

>> [T,Y] = meshgrid(tb,ty);
error: 'ty' undefined near line 1 column 21
>> [T,Y] = meshgrid(tb,yb);
>> dY = f(T,Y) ;
>> dT = ones(size(dY));
>> quiver(T,Y,dT,dY)
>> sol = @(t) 10*exp(-t/20);
>> xx = linspace(0,6);
>> hold on;
>> plot(xx,sol(xx))