# Error in writing an equation (sin function)

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verzhen Ligai on 8 May 2016
Commented: verzhen Ligai on 8 May 2016
Hello everyone,
I can't seem to successfully obtain a graph of the following equation: f(x,y)=sin(x)sin(y)/(x*y). I think it's because the equation is written wrongly but I can't seem to figure out what I did wrong.
Thank you.
>> x=linspace(0, 2*pi);
>> y=linspace(0, 2*pi);
>> [X,Y]=meshgrid(x,y);
>> Z=sin(X)*sin(Y)/(X*Y).;
>> meshz(X,Y,Z)

Roger Stafford on 8 May 2016
Edited: Roger Stafford on 8 May 2016
The line
Z=sin(X)*sin(Y)/(X*Y).;
is the trouble. You need dots there:
Z=sin(X).*sin(Y)./(X.*Y);
so as to produce element-by-element operations. As it stands. it is performing matrix multiplication and matrix division which you don’t want here. Also that trailing dot does not belong there.
Also note that at the single point x = 0 and y = 0 you will produce a NaN from a zero-divided-by-zero operation there.

verzhen Ligai on 8 May 2016
Thank you very much for your reply. I modified it and ran it again. However, the result graph is not what I expected. The graph that I wanted to get is shown in the black/white picture below. Thank you.
Walter Roberson on 8 May 2016
The diagram shows negative and positive coordinates, but you have only plotted over positive coordinates.
verzhen Ligai on 8 May 2016
Oh! that makes sense. You are right!!! 