I am trying to plot a 3D surface like the picture below to help depict the relationship between some variables. I have been fiddling with Google Search builtin plotter, trying different equations, but I do not have the knowledge to progress in this issue. I could go on trying random combinations of operators, but I thought maybe you could help...
The 3D surface should be something like this:
This is as far as I have got: $\sqrt{\frac {1}{\cos x + \sin y}}$, but I am sure there is a better way!
Can I have your help? Thank you very much.