I want to put the previously defined function independent of x (t) t s, using subs function but error, strives for the great god answer why and how should change, thank you!

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Set the function
%Syms s t.
T=1.5, 0.001, 1.5;
U1=stepfun (t, 0);
U2=stepfun (t, 1);
X=u1 - u2. % function u (t), u (t - 1)
The plot (t, x, 'k');

% variable displacement
Subs (x, t, s);


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Error using sym/subs> The normalize (line 231)
Entries in the second argument must be a scalar.

Error sym/subs> Mupadsubs (line 157)
[X2, Y2, symX symY]=the normalize (X, Y); % # ok

Error sym/subs (line 145)
G=mupadsubs (F, X, Y);

Error convolution (line 12)
Subs (x, t, s);