Surface generation with an external impact at particular point

I want to generate a surface using this code at a particular value of x and y, z will have a specific value otherwise it will be an array of zeros.

[t,r] = meshgrid(0:10:360,0:0.2:5);
[x,y] = pol2cart(t*pi/180,r);
if x=0:1;y=0:1;
    z=-90*x.^2*y.^2;
else
z=zeros(size(y));
end
surf(x,y,z)

[darova]

Can you make a sketch of a result you expect?

[Muhammad Mubashar saeed]

Answer 1

[darova]

See this

[t,r] = meshgrid(0:10:360,0:0.2:5);
[x,y] = pol2cart(t*pi/180,r);
z = -90*x.^2.*y.^2;     % remember about dot (.*)
ind = (0<x&x<1) & (0<y&y<1);
z(~ind) = 0;             % assign zeros 
surf(x,y,z)