# Doubt in plotting Vector Fields !

1. Dec 6, 2012

### iamnotageek

Hi,

I have a doubt in plotting the vector field.

In the post https://www.physicsforums.com/showthread.php?t=155579 it is mentioned that a vector field could be plotted for F (x,y) by, marking the (x,y) as the tail and F(x,y) as the head portion.

If so, then consider the function, F(x,y)=(x,y)

The, if the input is (2,4) then output is (2,4)

Then, if it plotted, there will be only points everywhere right? Because, the head and the tail portion is marked at the same point.

But, when I tried the same using a online plotter (http://cose.math.bas.bg/webMathematica/MSP/Sci_Visualization/VectorField [Broken]) , I got a different result, which I have attached.

#### Attached Files:

• ###### vector field for f(x,y)=(x,y).bmp
File size:
147.3 KB
Views:
61
Last edited by a moderator: May 6, 2017
2. Dec 6, 2012

### Staff: Mentor

Right.
It might be that the online graphing software doesn't handle zero vectors correctly.

Last edited by a moderator: May 6, 2017
3. Dec 6, 2012

### HallsofIvy

Staff Emeritus
No, that's not what I said. I said:
You are confusing points and vectors. If you use (x, y) to mean both the point (x,y) and the vector from point (0,0) to (x,y) then you are going to be confused! Since you learned to use (x, y) to mean a point way back in "pre-Calculus", it is better to use either <x, y> or xi+ yj to denote the vector. Then F(x, y)= <x, y> or, better, F(x, y)= xi+ yj. F(2, 4)= 2i+ 4j. With its "tail" at (2, 4), its head would be at (2+2, 4+ 4)= (4, 8).

Last edited by a moderator: May 6, 2017