"Z must be a matrix, not a scalar or vector." PLEASE HELP!

So this is the function I want graph using surf.m:

%simple multivariate function;
function [f]=ps2func(x1,x2)
if ((x1<=2) &&(x2<=2))
    f=4.*x1+3.*x2; %case 1 for the function
elseif ((x1>2) &&(x2>2))
    f=x1.^2+x2.^2; %case 2 for the function
else
    f=0; %case 3 for the function
end

%this is the suf.m function i used in an attempt to graph it: 
x1 = 1:.1:4;
x2 = 1:.1:4;
[X,Y] = meshgrid(x1,x2);
Z= [f]; 
mesh(X,Y,Z)
grid on
hold on

Answer 1

[Matt J]

You should have something like this:

x1 = 1:.1:4;
x2 = 1:.1:4;

mesh(x1,x2, ps2func(x1,x2) );

grid on
hold on

function f=ps2func(x1,x2)

 if isvector(x1), x1=x1(:);x2=x2(:).'; end
 
 f1=4.*x1+3.*x2; region1=(x1<=2) & (x2<=2);
 f2=x1.^2+x2.^2; region2=(x1>2) & (x2>2);
 
 f=false(size(f2));
 
 f(region1)=f1(region1);
 f(region2)=f2(region2);
 
end

[Kevin Zhou]

AWESOME! Thank u so much

Answer 2

[Rafael Hernandez-Walls]

x1 = 1:.1:4;
x2 = 1:.1:4;
[X,Y] = meshgrid(x1,x2);
Z= ps2func(X,Y); 
mesh(X,Y,Z)
grid on
hold on

function [f]=ps2func(x1,x2)
f=size(x1);
f=((x1<=2)&(x2<=2)).*(4.*x1+3.*x2)+((x1>2)&(x2>2)).*(x1.^2+x2.^2);