MATLAB: [t, x] = solve(‘x = 20t’, ‘x = 4t.^2/2’)

Symbolic Math Toolbox

|Error using symengine Invalid input. 'expression' is expected.

Error in sym>convertExpression (line 1449) s = mupadmex({x});

Error in sym>convertChar (line 1364) s = convertExpression(x);

Error in sym>tomupad (line 1164) S = convertChar(x);

Error in sym (line 163) S.s = tomupad(x);

Error in solve>getEqns (line 405) a = sym(a);

Error in solve (line 225) [eqns,vars,options] = getEqns(varargin{:});|

In the latest versions, the string (single quote) syntax is no longer supported.

syms t x 
[t, x] = solve(x == 20*t, x == 4*t.^2/2, [t,x])
t =
  0
 10
x =
   0
 200

Correct syntax:

syms t x
solve(t==(2*x+1)/(2*x-2),x)

producing:

ans =
(2*t + 1)/(2*t - 2)

I guess u is the unit-step function. You can try this if you have symbolic toolbox

syms t
x = 2*heaviside(-t/4+2);
fplot(x, [-10 10]);

Without symbolic toolbox

u = @(x) 1*(x>=0);
t = -10:0.01:10;
x = 2*u(-t/4+2);
plot(t, x)