what is the mistake i am doing here? i have to plot the three equations f,f1,f2

clc
clear all
syms x y z l1 l2 S1 S2 S3
f=2*x+4*y+z^2;
f1=y^2+z^2-1;
f2=x^2+z^2-1;
F=f+l1*f1+l2*f2;
dfx=diff(F,x);
dfy=diff(F,y);
dfz=diff(F,z);
[l1,l2,xc,yc,zc]=solve(f1,f2,dfx,dfy,dfz,'Real',true);
disp("Critical points are: ")

Critical points are: 

disp([xc,yc,zc])

disp('l1 and l2 are:')

l1 and l2 are:

disp([l1,l2])

a=size([xc,yc,zc]);
b=size([l1,l2]);
xc1=max(xc);
yc1=max(yc);
zc1=max(zc);
xc2=min(xc);
yc2=min(yc);
zc2=min(zc);
P=subs(F,{x,y,z},{xc1,yc1,zc1});
disp('maximum value is:')

maximum value is:

disp(P)

6

Q=subs(F,{x,y,z},{xc1,yc1,zc1});
disp('minimum value is:')

minimum value is:

disp(Q)

6

eqs = [f,f1,f2];
[S1,S2,S3]=solve(eqs,[S1,S2,S3]);
S1=double(S1);
S2=double(S2);
S3=double(S3);
plot3(f,f1,f2,{S1,S2,S3}) ;

Error using plot3
Data must be numeric, datetime, duration or an array convertible to double.

grid on
xlabel('x-axis')
ylabel('y-axis')
zlabel('z-axis')

error:

Error using plot3

Data must be numeric, datetime, duration or an array convertible to double.

Error in ass3q2 (line 35)

plot3(f,f1,f2,{S1,S2,S3}) ;

Answer 1

[Drishan Poovaya]

Hi,

It appears you are trying to plot symbolic functions. This is not what plot3 is designed to do, it can only plot numerical values. plot3(x,y,z) requires 3 equal lenght vectors where each triplet [ x(i) y(i) z(i) ] represents a point on the plot.

In order to plot symbolic functions I would suggest you read the following documentation for fplot and fsurf

https://www.mathworks.com/help/matlab/ref/fplot.html

https://www.mathworks.com/help/symbolic/fsurf.html