partial derivative

clc 
clear all
close all
syms x y  
z =input('Enter the two dimensional function f(x,y): ');
x1 = input('enter the x value at which the derivative has to be evaluated: ');
y1 = input('enter the y value at which the derivative has to be evaluated: '); 
%% Calculation of slope
z1 = subs(subs(z,x,x1),y,y1) 
ezsurf(z,[x1-2 x1+2]) 
f1 = diff(z,x) 
slopex = subs(subs(f1,x,x1),y,y1); 
%% Visualization of the plane 
[x2,z2]=meshgrid(x1-2:.25:x1+2,0:0.5:10); 
y2=y1*ones(size(x2)); 
hold on 
h1=surf(x2,y2,z2); 
set(h1,'FaceColor',[0.7,0.7,0.7],'EdgeColor','none') 
%% The tangent line
t=linspace(-1,1); 
x3=x1+t; 
y3=y1*ones(size(t)); 
z3=z1+slopex*t; 
line(x3,y3,z3,'color','blue','linewidth',2)