I want to plot!!!

[x,y]=meshgrid(-20:0.1:20);
m=2;
U=2;
a=4;
psi = U*y - (m/(2*pi))*(atan(y/(x-a))-atan(y/(x+a)));
contour(x,y,psi);

but I can't get my graphs. They are all blank page.

Answer 1

[Ameer Hamza]

You need to use element-wise division: https://www.mathworks.com/help/matlab/ref/rdivide.html

[x,y]=meshgrid(-20:0.1:20);
m=2;
U=2;
a=4;
psi = U*y - (m/(2*pi))*(atan(y./(x-a))-atan(y./(x+a)));
                             %^ dot here and ^ here
contour(x,y,psi);

[혜승 주]

This really helped!! Thanks a lot!! 8ㅁ8

Answer 2

[dpb]

You left out some very key information MATLAB told you about...

...
contour(x,y,psi);
Warning: Matrix is singular to working precision. 
 
Warning: Matrix is singular to working precision. 
 
Warning: Contour not rendered for non-finite ZData 
>> In contour (line 51) 

That's a very big klew you didn't do something right!!!

And, what that is, is that you used the ordinary '*' and '/' operators in defining psi when you wanted and needed the dot operators for element-by-element operations. Use

psi = U*y - (m/(2*pi)).*(atan(y./(x-a))-atan(y./(x+a)));

instead and joy will ensue...

[혜승 주]

I should carefully read those! Thank you!!