I am try to show a simple plane wave by DensityPlot the real part of $e^{ikr}$, $k=(k_x,k_y)$, $r=(x,y)$.
DensityPlot[Cos[(3 x + 4 y)], {x, -10, 10}, {y, -10, 10},
PlotRange -> {{-10, 10}, {-10, 10}}, Frame -> False,
ColorFunction -> "BlueGreenYellow", WorkingPrecision -> 100]
Here $k=(3,4)$, It is supposed to be a clear stripe, however there is something wrong with the image as I show below.
Then I tried to change $k$ to $k=(1,1)$, this time it looks correct.
DensityPlot[Cos[(x + y)], {x, -10, 10}, {y, -10, 10},
PlotRange -> {{-10, 10}, {-10, 10}}, Frame -> False,
ColorFunction -> "BlueGreenYellow", WorkingPrecision -> 100]
I am wondering why it happens and how to change the code?