3d Plot of a function

Dear there,

I have a piecewise function u(x,t) as following code. I want to plot u(x,t) on the region (x,t) ∈ [-1,1]x[-2,2] by using the contour surface plot as the link

Could you help me please?

Thanks

clc;
clear all;
syms x t 
 t1 = exp(x);
t21 = -5 .* t;
t3 = exp(t21);
t5 = exp((1 + t21));
t4 = ((0 <= t & t <= 1/2) .* 1.73205);
t5 = ((0 <= t & t <= 1/2) .* (30.9839 .* t - 7.74597));
t6 = ((1/2 <= t & t <= 1) .* 1.73205);
t7 = ((1/2 <= t & t <= 1) .* (30.9839 .* t - 23.2379));
t6 = (1 + t5).^2;
t2 = 1 ./ t6;
t7 = (1 + t3).^2;
t3 = 1 ./ t7;
t8 = -0.00399646;
t9 = 0.00922094;
t10 = 0.0415432;
t11 = 0.0603743;
t12 = 0.177671;
t13 = ((0 <= x & x <= 1/2) .* 1.73205);
t14 = ((0 <= x & x <= 1/2) .* (30.9839 .* x - 7.74597));
t15 = ((1/2 <= x & x <= 1) .* 1.73205);
t16 = ((1/2 <= x & x <= 1) .* (30.9839 .* x - 23.2379));
t8 = (1 + t1).^2;
t1 = 1 ./ t8;
u = -1/4 + (-0.00243052 .* t13 - 0.000809061 .* t14 - 0.00195593 .* t16 - 0.0152378 .* t15) .* t4 + (-0.00043359 .* t13 - 0.000146113 .* t14 - 0.000477063 .* t16 - 0.00319022 .* t15) .* t5 + (-0.00276115 .* t13 - 0.000933166 .* t14 - 0.00314361 .* t16 - 0.0207985 .* t15) .* t6 + t7 .* (0.000172747 .* t13 + 0.0013619 .* t15 + 0.00021141 .* t16 + 5.86775e-05 .* t14) + x .* (t10 .* t4 + t11 .* t6 + t5 .* t9 + t7 .* t8 + t12 + t2 - t3) + t3 + t1;

Answer 1

[Walter Roberson]

create a meshgrid of x and t values, X and T. Then

Z = double(subs(u, {x, t}, {X, T})) ;
surfc(X, Y, Z)

[student_md]

I wrote a code as follows

x=0:0.1:1;
t=0:0.1:2; 
  
[X,T]=meshgrid(x,t); 
Z = double(subs(u, {x, t}, {X, T})) ;

surfc(X, T, Z); 

But I get the following error: What is wrong?

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

Error in piecewise3dplot (line 33)
Z = double(subs(u, {x, t}, {X, T})) ;

[student_md]

Dear @Walter Roberson?

[Walter Roberson]

xvec = 0:0.1:1;
tvec = 0:0.1:2; 
  
[X,T] = meshgrid(xvec, tvec); 
Z = double(subs(u, {x, t}, {X, T})) ;

You were overwriting the symbolic nature of x and t with numeric variables, so they were no longer the names of symbolic variables when you got to the subs() statement.

[student_md]

xvec = 0:0.1:1;
tvec = 0:0.1:2; 
  
[X,T] = meshgrid(xvec, tvec); 
Z = double(subs(u, {x, t}, {X, T})) 

But the code is not still working...When I run the your last code, I get the following errors: I found some solutions of the errors on this link. But I can' t solve and still have errors.

 Error in sym/double (line 707)
        Xstr = mupadmex('symobj::double', S.s, 0);

Error in piecewise3dplot (line 31)
Z =  double(subs(u, {x, t}, {X, T}));
 

[Walter Roberson]

syms x t 
 t1 = exp(x);
t21 = -5 .* t;
t3 = exp(t21);
t5 = exp((1 + t21));
t4 = ((0 <= t & t <= 1/2) .* 1.73205);
t5 = ((0 <= t & t <= 1/2) .* (30.9839 .* t - 7.74597));
t6 = ((1/2 <= t & t <= 1) .* 1.73205);
t7 = ((1/2 <= t & t <= 1) .* (30.9839 .* t - 23.2379));
t6 = (1 + t5).^2;
t2 = 1 ./ t6;
t7 = (1 + t3).^2;
t3 = 1 ./ t7;
t8 = -0.00399646;
t9 = 0.00922094;
t10 = 0.0415432;
t11 = 0.0603743;
t12 = 0.177671;
t13 = ((0 <= x & x <= 1/2) .* 1.73205);
t14 = ((0 <= x & x <= 1/2) .* (30.9839 .* x - 7.74597));
t15 = ((1/2 <= x & x <= 1) .* 1.73205);
t16 = ((1/2 <= x & x <= 1) .* (30.9839 .* x - 23.2379));
t8 = (1 + t1).^2;
t1 = 1 ./ t8;
u = -1/4 + (-0.00243052 .* t13 - 0.000809061 .* t14 - 0.00195593 .* t16 - 0.0152378 .* t15) .* t4 + (-0.00043359 .* t13 - 0.000146113 .* t14 - 0.000477063 .* t16 - 0.00319022 .* t15) .* t5 + (-0.00276115 .* t13 - 0.000933166 .* t14 - 0.00314361 .* t16 - 0.0207985 .* t15) .* t6 + t7 .* (0.000172747 .* t13 + 0.0013619 .* t15 + 0.00021141 .* t16 + 5.86775e-05 .* t14) + x .* (t10 .* t4 + t11 .* t6 + t5 .* t9 + t7 .* t8 + t12 + t2 - t3) + t3 + t1;

U = matlabFunction(u);

xvec = 0:0.1:1;
tvec = 0:0.1:2; 
  
[X,T] = meshgrid(xvec, tvec);
Z = U(X,T);

surf(X, T, Z)