3D Surface Plot Showing Flat Surface

Hi all,

Completely new to MATLAB but have been asked to produce 3D plot of the function z = x + 2xy² + 3x for x and y values of 0 to 15. I have followed tutorials online showing how to produce a surface plot and entered the attached script but my end result is a flat plane and I've tried it many times. I produced the same graph on excel for comparison and it was completely different (it was actually 3D). Can someone please explain how to solve this in a manner a beginner would understand?

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>> x=[0:1:15];
>> y=[0:1:15];
>> [xx,yy]=meshgrid(x,y);
>> zz=xx+(2*xx*yy.^2)+3*xx;
>> surf(xx,yy,zz);

[Rena Berman]

(Answers Dev) Restored edit

Answer 1

[Ahmet Cecen]

You for got a dot somewhere:

 x=[0:1:15];
 y=[0:1:15];
 [xx,yy]=meshgrid(x,y);
 zz=xx+(2*xx.*yy.^2)+3*xx; % HERE
 surf(xx,yy,zz);