I have run into trouble with a Plot3D problem. My code is following:
eqn = D[u[x, t], t] == D[D[u[x, t], x], x];
ic = {u[x, 0] == 1, u[0, t] == 0, Derivative[1, 0][u][10, t] == 0};
dsol = DSolve[{eqn, ic}, u, {x, t}];
Plot3D[u[x, t], {x, 0, 100}, {t, 0, 100}, ColorFunction -> "RustTones", Mesh -> All];
and the same problem happens in another Plot code:
linearsystem = {x'[t] == -3 x[t] + 2 y[t], y'[t] == x[t] - 4 y[t]};
initialvalues = {x[0] == 1, y[0] == 3};
sol2 = NDSolve[Join[linearsystem, initialvalues], {x, y}, {t, 0, 3}];
Plot[{x[t], y[t]}, {t, 0, 3}];
When I click "shift+return", it just results in an empty graph in both of these two codes. I don't know what is wrong with my code. Could anyone help me?
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