# built in method norm of Vector_symbolic_dense object

So, I want to write a program that plots equipotential contours for z=0 for electric potential of 3 charges(ch) at specified coordinates(matrix m). I need rv to be a vector with general coordinates so I can later plot the equipotential contours.

```
var(' x y ')
m=matrix(QQ,[[1,1],[-1,-1],[-1,1]])
ch=([-1,1,1])
rv=vector([x,y])
k=m.nrows();
u=[(rv-m[i]).norm() for i in range(k)];
```

However, after the last line I get this:

```
[<built in method norm of Vector_symbolic_dense object at 0xbb752fc>, <built in method norm of Vector_symbolic_dense object at 0xbb7532c>, <built in method norm of Vector_symbolic_dense object at 0xbb750bc>]
```

How do I fix this to get the norm of rv-m[i]?

,

Which version of Sage are you running ? I got the following:

Are your shure this is the code in your worksheet? It seems like you left out the parenthesis in .norm()

It's a mistake I made here, there is the parenthesis in .norm() in my worksheet

And I'm using sage 5.13 because newer versions don't work on my virtualbox machine.

That seems odd about the virtual box. Can you give more specific details in another question (or, better, on sage-support@googlegroups.com)?