[jitter] visualisation of a (x,y) vector field

Hi, 

I'm trying to visualize an (x,y) vector field (like here http://mathworld.wolfram.com/VectorField.html)
Something is going wrong though, specifically at the jit.op @op +, but I can't seem to figure out how to solve it... 
any pointers ?

grtz. 

Brecht . 


max v2;
#N vpatcher 431 44 954 472;
#P origin 0 -2;
#P window setfont "Sans Serif" 9.;
#P window linecount 1;
#N vpatcher 30 89 161 286;
#P outlet 8 116 15 0;
#P window setfont "Sans Serif" 9.;
#P message 8 96 70 196617 fullscreen \$1;
#P toggle 8 73 15 0;
#P newex 8 48 52 196617 select 32;
#P newex 8 25 40 196617 key;
#P connect 0 0 1 0;
#P connect 1 0 2 0;
#P connect 2 0 3 0;
#P connect 3 0 4 0;
#P pop;
#P newobj 10 143 25 196617 p fs;
#P newex 34 102 41 196617 s pulse;
#P newex 10 164 256 196617 jit.window vectors @floating 1 @fsaa 0 @fsmenubar 0;
#P toggle 10 31 15 0;
#P newex 10 76 58 196617 t b b erase;
#P newex 10 56 57 196617 qmetro 20;
#P newex 10 123 204 196617 jit.gl.render vectors @erase_color 0 0 0 1;
#P newex 11 258 118 196617 jit.op @op - @val 0.375;
#P newex 67 335 64 196617 jit.op @op +;
#P newex 121 315 279 196617 jit.expr @expr "0.1*cos(in[0].p[0])" "0.1*sin(in[0].p[1])";
#P newex 121 294 207 196617 jit.expr @expr "atan(in[0].p[1]/in[0].p[0]";
#P flonum 131 258 35 9 0 0 0 3 0 0 0 221 221 221 222 222 222 0 0 0;
#P number 56 197 35 9 0 0 0 3 0 0 0 221 221 221 222 222 222 0 0 0;
#P message 56 216 56 196617 dim \$1 \$1;
#P newex 11 378 183 196617 jit.gl.mesh vectors @draw_mode lines;
#P newex 11 357 66 196617 jit.multiplex;
#P newex 11 217 41 196617 r pulse;
#P newex 11 237 139 196617 jit.gencoord 2 float32 10 10;
#P comment 36 145 107 196617 spacebar = fullscreen;
#P comment 330 295 100 196617 calculate direction;
#P comment 401 316 100 196617 add length;
#P connect 17 0 15 0;
#P connect 15 0 16 0;
#P fasten 16 2 14 0 63 97 15 97;
#P connect 16 0 14 0;
#P connect 20 0 18 0;
#P fasten 7 0 3 0 61 235 16 235;
#P connect 4 0 3 0;
#P connect 3 0 13 0;
#P connect 13 0 5 0;
#P connect 5 0 6 0;
#P connect 16 1 19 0;
#P connect 8 0 7 0;
#P fasten 13 0 12 0 16 305 72 305;
#P connect 12 0 5 1;
#P connect 9 0 13 1;
#P fasten 13 0 10 0 16 284 126 284;
#P connect 10 0 11 0;
#P connect 11 0 12 1;
#P pop;