Hi, Can someone help me?

I am trying to calculate the angle between two vectors, but the only results I get are "NaN". I am sure it is something I am doing wrong...

     
v=new SimpleVector(0,0,0);
ov=new SimpleVector(1,1,10);
float angle = v.calcAngle(ov);
Logger.log("angle:"+String.valueOf(angle));


The Android Monitor just outputs:

I/jPCT-AE: angle:NaN