[jitter] getcell equivalent in jit.expr?

This sort of thing isn't possible within jit.expr syntax (without 
leveraging instances of jitter objects), but is pretty simple to do 
within an abstraction using jit.matrix.

Something like the following should work:
#P user jit.pwindow 19 318 82 62 0 1 0 0 1 0;
#P window setfont "Sans Serif" 9.;
#P window linecount 1;
#P newex 20 88 134 196617 jit.noise 1 float32 320 240;
#P button 180 34 15 0;
#P newex 180 49 45 196617 loadbang;
#P newex 180 69 134 196617 jit.matrix 1 float32 512 1;
#P newex 180 89 194 196617 jit.expr @expr "abs(sin(norm[0]*10))";
#P newex 20 296 141 196617 jit.expr @expr "in[0]*in[1]";
#P number 134 143 35 9 0 0 0 3 0 0 0 221 221 221 222 222 222 0 0 0;
#P newex 134 196 134 196617 jit.matrix 1 float32 512 1;
#P newex 134 163 27 196617 t b i;
#P message 151 218 144 196617 srcdimstart \$1 \, srcdimend \$1;
#P newex 151 246 175 196617 jit.matrix 1 float32 1 @usesrcdim 1;
#P toggle 20 44 15 0;
#P newex 20 68 64 196617 qmetro 50;
#P window linecount 2;
#P comment 196 140 141 196617 this seems easier than trying to wrangle 
jit.expr syntax.;
#P user panel 114 131 232 146;
#X brgb 255 255 255;
#X frgb 205 219 224;
#X border 4;
#X rounded 0;
#X shadow 0;
#X done;
#P connect 14 0 9 0;
#P connect 2 0 14 0;
#P connect 9 0 15 0;
#P fasten 7 0 4 0 139 237 156 237;
#P connect 12 0 11 0;
#P connect 13 0 12 0;
#P fasten 10 0 7 0 185 185 139 185;
#P connect 11 0 10 0;
#P connect 4 0 9 1;
#P connect 8 0 6 0;
#P connect 6 0 7 0;
#P connect 6 1 5 0;
#P connect 5 0 4 0;
#P connect 3 0 2 0;
#P window clipboard copycount 16;