why are my surfaces not connected?

i used the following coding to plot the surfaces as shown below but why are my surfaces not connected although i used the end line of the first surface as the first line of my second surface?

clc
clear all
close all

%control point for first surface
P0 = [0 0 0]; P1 = [1 0 0]; P2 = [2 0 0]; P3 = [3 0 0];
P4 = [0 1 0]; P5 = [1 1 2]; P6 = [2 1 2]; P7 = [3 1 0];
P8 = [0 2 0]; P9 = [1 2 2]; P10 = [2 2 2]; P11 = [3 2 0];
P12 = [0 3 0]; P13 = [1 3 0]; P14 = [2 3 0]; P15 = [3 3 0];

phi=1;%scaling factor
B1=1;%shape parameter lambda 
B2=1;%shape parameter miu
G17=phi*((2+B1)/(2+B2))*(P3-P2)+P3
G21=phi*((2+B1)/(2+B2))*(P7-P6)+P7
G25=phi*((2+B1)/(2+B2))*(P11-P10)+P11
G29=phi*((2+B1)/(2+B2))*(P15-P14)+P15

%control point for second surface
P3; G17; P18 = [5 0 0]; P19 = [6 0 0];
P7; G21; P22 = [5 1 0]; P23 = [6 1 0];
P11; G25; P26 = [5 2 0]; P27 = [6 2 0];
P15; G29; P30 = [5 3 0]; P31 = [6 3 0];

Gx=[P0(1) P1(1) P2(1) P3(1);P4(1) P5(1) P6(1) P7(1);P8(1) P9(1) P10(1) P11(1);P12(1) P13(1) P14(1) P15(1)];
Gy=[P0(2) P1(2) P2(2) P3(2);P4(2) P5(2) P6(2) P7(2);P8(2) P9(2) P10(2) P11(2);P12(2) P13(2) P14(2) P15(2)];
Gz=[P0(3) P1(3) P2(3) P3(3);P4(3) P5(3) P6(3) P7(3);P8(3) P9(3) P10(3) P11(3);P12(3) P13(3) P14(3) P15(3)];

Gx1=[P3(1) G17(1) P18(1) P19(1);P7(1) G21(1) P22(1) P23(1);P11(1) G25(1) P26(1) P27(1);P15(1) G29(1) P30(1) P31(1)];
Gy1=[P3(2) G17(2) P18(2) P19(2);P7(2) G21(2) P22(2) P23(2);P11(2) G25(2) P26(2) P27(2);P15(2) G29(2) P30(2) P31(2)];
Gz1=[P3(3) G17(3) P18(3) P19(3);P7(3) G21(3) P22(3) P23(3);P11(3) G25(3) P26(3) P27(3);P15(3) G29(3) P30(3) P31(3)];

N=20;
t=(1:N)'/N;
p=(pi/2)*t;
T=[p.^0 sin(p) (sin(p).^2) (sin(p).^3) cos(p) (cos(p).^2) (cos(p).^3)];

       
    A=[1 0 0 1;
       -(B1+2) (2+B1) 0 0;
       ((2*B1)+1) -(2+2*B1) 0 0;
       -B1 B1 0 0;
       0 0 2+B2 -(B2+2);
       0 0 -((2*B2)+2) ((2*B2)+1);
       0 0 B2 -B2];
       
 
TT=transpose(T);
AA=transpose(A);
z1 = T*A*Gx*AA*TT;
z2 = T*A*Gy*AA*TT;
z3 = T*A*Gz*AA*TT;

z4 = T*A*Gx1*AA*TT;
z5 = T*A*Gy1*AA*TT;
z6 = T*A*Gz1*AA*TT;

surf(z1,z2,z3);
hold on;
surf(z4,z5,z6);
hold on;

Answer 1

[KSSV]

You have to merge them. As of now they are two independent surfaces. Do the below:

X = [z1 z4] ;
Y = [z2 z5] ;
Z = [z3 z6] ;

surf(X,Y,Z)

[NurFadhilah Samsuddin]

i tried and it works! thank you!