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plotting - How to prepare data for ListVectorPlot[]?


I was trying to plot a few velocity vectors measured at given points. However I am unable to do this with ListVectorPlot[] function. I get error each time I try to use it (it says: VisualizationCoreListVectorPlot::vfldata: {{{1,1},{2,2}}} is not a valid vector field dataset or a valid list of datasets.). Finally I succeeded using Arrow[] graphics entity, but I'd rather use ListVectorPlot[] function.


Lets say I have three


points={{1,1},{2,1},{3,1}}

and 2D vectors measured in that points:


vec={{1,0},{0.7,0.1},{1,-0.1}}


How to prepare data to plot this using ListVectorPlot to get such an image:


Arrows obrained by the following code:


Code used to plot arrows:


ar = {
  Graphics[Arrow[{{1, 1}, {1 + 1, 1 + 0}}]], 
  Graphics[Arrow[{{2, 1}, {2 + 0.7, 1 + 0.1}}]], 
  Graphics[Arrow[{{3, 1}, {3 + 1, 1 - 0.1}}]]
}; 
Show[ar]


Answer



Let me explain the error message first. You assumed that you can give a list of points and vectors and ListVectorPlot draws exactly those vectors. This is not the case. If you give ListVectorPlot 4 vectors on the corner of the unit-square, it will do the following:


ListVectorPlot[{
  {{0, 0}, {1, 1}}, 
  {{1, 0}, {-1, 0}},
  {{1, 1}, {-1, -1}}, 
  {{0, 1}, {-1, 0}}}]

Mathematica graphics


See that it interpolates all values in between? And here is the problem with your dataset. All your vectors lie on a line which makes it impossible to create a 2d-plot.



Therefore, are you sure you want to use ListVectorPlot? What you try can be achieved in one line of code (no matter how many points and vectors you have!)


Graphics[Arrow[{#1, #1 + #2}] & @@@ Transpose[{points, vec}]]

Mathematica graphics


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